PROCESS FOR PREPARING V-Ti-P CATALYSTS FOR SYNTHESIS OF 2,3-UNSATURATED CARBOXYLIC ACIDS

ABSTRACT

The invention relates to a catalyst composition comprising a mixed oxide of vanadium, titanium, and phosphorus. The titanium component is derived from a water-soluble, redox-active organo-titanium compound. The catalyst composition is highly effective at facilitating the vapor-phase condensation of formaldehyde with acetic acid to generate acrylic acid, particularly using an industrially relevant aqueous liquid feed. Additionally, the catalyst composition is catalytically active towards the formation of acrylic acid from methylene diacetate and methacrylic acid from methylene dipropionate; both reactions are carried out with high space time yields.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Non-Provisional applicationSer. No. 13/826,180, filed Mar. 14, 2013, which is continuation-in-partof U.S. patent application Ser. No. 13/234,313 filed Sep. 16, 2011, nowU.S. Pat. No. 8,765,629, the entireties of which are incorporated hereinby reference.

FIELD OF THE INVENTION

The invention generally relates to the field of catalysis and, inparticular, to mixed oxide catalysts for the preparation of2,3-unsaturated carboxylic acids. The invention further relates to thepreparation of 2,3-unsaturated carboxylic acids using a methylenedialkanoate feed with a mixed oxide catalyst.

BACKGROUND OF THE INVENTION

2,3-Unsaturated carboxylic acids and esters can be prepared from thereaction of a formaldehyde (H₂CO) source and a saturated carboxylic acidor ester containing one less carbon atom. Thus, acrylic and methacrylicacid derivatives can be prepared from the condensation of a formaldehydesource with acetic or propionic acid derivatives, respectively. Thereaction produces one equivalent of water for each equivalent ofcarboxylic acid derivative reacted.

Although a number of catalysts have been proposed for this reaction,catalysts containing acidic vanadium and phosphorus oxides are among themost efficient, especially when a third component such as titanium orsilicon is present in the catalyst. Water, however, tends to inhibit thecondensation reaction with these catalysts. The use of formalin—whichtypically contains about 37 weight percent formaldehyde in water—as astarting material, therefore, is less efficient. Methanol can also be aninhibitor for the condensation reaction, and, since formalin can alsocontain methanol, the efficiency can be further lowered. When acarboxylic acid is the reactant, the presence of methanol in formalincan create a mixture of acids and methyl esters. And when an ester isthe reactant, the water in formalin can create a mixture of acids andesters.

Industrial grade aqueous formaldehyde contains about 55 weight percentformaldehyde. It is relatively inexpensive and, therefore, is aneconomical source of this reactant. Thus, there is a need in the art forcatalysts that are capable of condensing formaldehyde with alkanoicacids or esters in the vapor phase and that are tolerant of water in thefeedstock. Ideally, such catalysts would also provide a high conversionof formaldehyde along with a high selectivity to the acrylic product.

The conventional process for these aldol condensation reactions combinesa formaldehyde source, such as trioxane, with a carboxylic acid to formwater, the 2,3-unsaturated carboxylic acid, and formaldehyde. Theformaldehyde can react with itself at any time during the reaction toform paraformaldehyde. This by-product formation of paraformaldehyde cancontribute to yield losses and increased maintenance costs as theparaformaldehyde deposits on equipment and piping.

Conventional Feed

The problems caused by paraformaldehyde create the need to make2,3-unsaturated carboxylic acids without producing significantparaformaldehyde. One solution is to introduce a methylene unit by analternative feed that does not utilize or produce formaldehyde which canpolymerize to paraformaldehyde. A methylene dialkanoate feed can be usedas such an alternative feed.

Methylene Dialkanoate Feed

The use of a methylene dialkanoate feed can also lead to improved spacetime yield (STY) while operating at decreased temperatures, even in thepresence of extraneous water when compared to the conventional reactionprocess. These reaction improvements come as a surprise since acrylicacid production from conventional feeds comprising acetic acid andformaldehyde (as trioxane) are negatively impacted by water and reducedtemperature. The practical utility of these benefits are increasedcatalyst lifetime and maintained STY when water is introduced to thereaction system from impure gas lines or generated via by-productchemistry.

Although the V—Ti—P catalysts of the present invention function with thepresence of water, improved STY can be seen by attenuating the effectsof water. One approach to reduce the presence of water in the feed is toreplace aqueous formaldehyde with anhydrous formaldehyde (trioxane,C₃H₆O₃). Despite this replacement, the molar addition of trioxane withacetic acid still includes one mole of a latent molecular water, therebylimiting the maximum attainable rate. To further offset the effect ofwater, methylene dialkanoates, such as methylene diacetate (MDA) andmethylene dipropionate (MDP) can be synthesized from formaldehyde andutilized as a feed towards the production of acrylic acid andmethacrylic acid, respectively. These methylene dialkanoates aremolecularly equivalent to one mole of formaldehyde and two moles of thecorresponding carboxylic acid but without the latent molecular water(i.e. one mole of latent water is not produced). MDA and MDP formacrylic acid and methacrylic acid, respectively, over the V—Ti—Pcatalyst at a surprisingly high reaction rate and yield.

Vanadium-titanium-phosphorus (V—Ti—P) mixed oxides are the best knowncatalysts for generating acrylic acid from the condensation offormaldehyde and acetic acid. But the preparation of these catalysts canbe dangerous and is not amenable to scale-up. Typically, the titaniumcomponent is incorporated into these catalysts by first hydrolyzingliquid titanium chloride. This step, unfortunately, generates largequantities of hydrochloric acid fumes. Thus, there is also a need in theart for methods of preparing V—Ti—P mixed oxide catalysts that are saferand more amenable to industrial production.

The present invention addresses these needs as well as others that willbe apparent from the following description and claims.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a catalyst compositioncomprising a mixed oxide of vanadium (V), titanium (Ti), and phosphorus(P). The titanium component of the catalyst composition is derived froma water-soluble, redox-active organo-titanium compound.

In a second aspect, the present invention provides a method forpreparing a catalyst composition comprising a mixed oxide of vanadium(V), titanium (Ti), and phosphorus (P). The method comprises the stepsof:

-   -   (a) providing an aqueous solution comprising a water-soluble,        redox-active organo-titanium compound;    -   (b) adding a vanadium compound and a phosphorus compound to the        aqueous titanium solution to form a mixture of catalyst        components;    -   (c) heat-treating the mixture;    -   (d) removing water from the heat-treated mixture to obtain a        solid residue comprising the catalyst components; and    -   (e) calcining the solid residue at an elevated temperature in        the presence of air to obtain the catalyst composition.

In a third aspect, the present invention provides a process forpreparing a 2,3-unsaturated carboxylic acid. The process comprises thestep of contacting a formaldehyde source with a carboxylic acid in thepresence of a condensation catalyst under vapor-phase condensationconditions to obtain the 2,3-unsaturated carboxylic acid. Thecondensation catalyst comprises a mixed oxide of vanadium (V), titanium(Ti), and phosphorus (P). The titanium component of the condensationcatalyst is derived from a water-soluble, redox-active organo-titaniumcompound.

In a fourth aspect, the present invention provides a process forpreparing a 2,3-unsaturated carboxylic acid. The process comprises thesteps of contacting a methylene dialkanoate and a diluent gas with acondensation catalyst under vapor-phase condensation conditions toobtain the 2,3-unsaturated carboxylic acid. The condensation catalystcomprises a mixed oxide of vanadium (V), titanium (Ti), and phosphorus(P). The methylene dialkanoate has the general formula (I):

wherein R is selected from the group consisting of hydrogen and an alkylgroup having 1 to 8 carbon atoms.

In a fifth aspect, the present invention provides a process forpreparing a 2,3-unsaturated carboxylic acid. The process comprises thestep of contacting a methylene dial kanoate and a diluent gas with acondensation catalyst under vapor-phase condensation conditions toobtain the 2,3-unsaturated carboxylic acid. The condensation catalystcomprises a mixed oxide of vanadium (V), titanium (Ti), and phosphorus(P). The titanium component is derived from a water-soluble,redox-active organo-titanium compound. The methylene dialkanoate has thegeneral formula (I):

wherein R is selected from the group consisting of hydrogen, methyl,ethyl, propyl, and isopropyl.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the X-ray diffraction pattern of the amorphouscatalyst prepared via Method A in Example 1.

FIG. 2 is a graph showing the X-ray diffraction pattern of the amorphouscatalyst prepared via Method B in Comparative Example 1.

FIG. 3 is a graph showing the X-ray diffraction pattern of the mixedamorphous-crystalline (TiO₂) catalyst prepared via Method C inComparative Example 2.

FIG. 4 is a graph showing the X-ray diffraction pattern of thecrystalline [VO(HPO₄)(H₂O)_(0.5)] catalyst prepared via Method D inComparative Example 3.

FIG. 5 is a graph showing the X-ray diffraction pattern of thecrystalline catalyst [(VO)₂(P₂O₇)] prepared via Method E in ComparativeExample 4.

FIG. 6 is a graph showing the X-ray diffraction pattern of thecrystalline catalyst (TiO₂) prepared via Method F in Comparative Example5.

FIG. 7 is a graph showing the X-ray diffraction pattern of the amorphouscatalyst prepared via Method G in Example 2.

FIG. 8 is a graph showing the X-ray diffraction pattern of thecrystalline catalyst [V(PO₃)₃ and Ti(P₂O₇)] prepared via Method H inComparative Example 6.

FIG. 9 is a graph showing the X-ray diffraction pattern of the amorphouscatalyst prepared via Method I in Example 5.

FIG. 10 is a graph showing the X-ray diffraction pattern of theamorphous catalyst prepared via Method J in Example 6.

DETAILED DESCRIPTION OF THE INVENTION

It has been surprisingly discovered that V—Ti—P mixed oxide catalystscan be prepared from a water-soluble, redox-active organo-titaniumsource. Employing such a titanium source can provide an inherentlysafer, and more practical and rapid route to V—Ti—P materials. Inaddition, it has been surprisingly discovered that the resultingcatalysts can have a higher surface area and acidity, and can be moreactive for acrylic acid formation when an aqueous formaldehyde sourceand acetic acid are used as the feed. Moreover, it has been surprisinglydiscovered that the resulting catalyst can be even more active for theformation of acrylic acid and methacrylic acid from MDA and MDP,respectively.

Thus, in a first aspect, the present invention provides a catalystcomposition comprising a mixed oxide of vanadium (V), titanium (Ti), andphosphorus (P). The titanium component of the catalyst composition isderived from a water-soluble, redox-active organo-titanium compound(sometimes referred to herein as simply “water-soluble titaniumcompound,” “organo-titanium compound,” or “titanium compound”).

As used herein, the term “and/or,” when used in a list of two or moreitems, means that any one of the listed items can be employed by itself,or any combination of two or more of the listed items can be employed.For example, if a composition is described as containing components A,B, and/or C, the composition can contain A alone; B alone; C alone; Aand B in combination; A and C in combination; B and C in combination; orA, B, and C in combination.

It is to be understood that the mention of one or more process stepsdoes not preclude the presence of additional process steps before orafter the combined recited steps or intervening process steps betweenthose steps expressly identified. Moreover, the lettering of processsteps or ingredients is a convenient means for identifying discreteactivities or ingredients and the recited lettering can be arranged inany sequence, unless otherwise indicated.

By “water-soluble,” it is meant that the organo-titanium compound candissolve in water at 20° C. and 1 atm absolute (101.325 kPa) to form ahomogeneous solution of at least 1 weight percent of the organo-titaniumcompound. Preferably, the compound can dissolve in water to form ahomogeneous solution of at least 25 weight percent. More preferably, thecompound can dissolve in water to form a homogeneous solution of atleast 40 weight percent.

By “redox-active,” it is meant that the organic ligand of theorgano-titanium compound is capable of reducing the oxidation state ofvanadium from +5 to +4, +5 to +3, or +4 to +3. Alternatively, theorgano-titanium compound is “redox-active” if the derivative of theorgano-titanium compound, in the aqueous mixture used to make thecatalyst, is capable of reducing the oxidation state of vanadium from +5to +4, +5 to +3, or +4 to +3.

Examples of water-soluble, redox-active organo-titanium compoundsinclude titanium lactates, titanium alkanolamines, and titaniumacetylacetonates. Such compounds are commercially available, such asfrom Dorf Ketal under the trade name TYZOR®. Practical examples of suchcompounds include titanium(IV) bis(ammonium lactate)dihydroxide(TBALDH), titanium diethanolamine, titanium triethanolamine, andtitanium acetylacetonate. In one aspect, the organo-titanium compoundcomprises titanium(IV) bis(ammonium lactate)dihydroxide.

The catalyst composition according to the present invention can have thegeneral formula VTi_(a)P_(b)O_(c), wherein a=0.3 to 6.0, preferably 1.0to 4.0; b=2.0 to 13.0, preferably 4.0 to 10.0; and c is the number ofatoms required to satisfy the valences of the components other thanoxygen.

The catalyst composition of the invention can be supported on an oxidesupport. Suitable oxide supports include silica, alumina, titaniumoxide, zirconium oxide, and titanium or zirconium pyrophosphates. Otheroxide supports may be used provided that they are inert to the desiredcatalytic reaction. The supports should be physically robust andpre-shaped. The term “pre-shaped” is used in this context to mean thatthe shape of the final catalyst is essentially the same as the startingsupport. The pre-shaped oxides typically can have average particlediameter sizes ranging from about 0.1 millimeter (mm) to about 20 mm.They can be in any common form such as extrudates, compressed pellets,or bulk solid that has been pulverized to the desired mesh size. Theymay also be in a variety of shapes such as rods, stars, cylinders,spheres, or broken chunks.

The catalyst composition according to the present invention can beprimarily amorphous in structure. One skilled in the art recognizes thatan amorphous catalyst composition can have a small amount of crystallinestructure caused, for example, by impurities. By “amorphous” or“primarily amorphous” it is meant that the catalyst composition containsless than 10 weight percent crystalline material. The percentcrystallinity is calculated based on the integrated intensities of anX-Ray diffraction from the individual diffraction patterns with peaks ofcrystallite size greater than 30 Å defined as crystalline and peaks ofcrystallite size less than or equal to 30 Å defined as amorphous.

In accordance with a second aspect of the invention, the catalystcomposition according to the present invention can be prepared using thefollowing general steps:

-   -   (f) providing an aqueous solution comprising the water-soluble,        redox-active organo-titanium compound;    -   (g) adding a vanadium compound and a phosphorus compound to the        aqueous titanium solution to form a mixture of catalyst        components;    -   (h) heat-treating the mixture;    -   (i) removing water from the heat-treated mixture to obtain a        solid residue comprising the catalyst components; and    -   (j) calcining the solid residue at an elevated temperature in        the presence of air to obtain the catalyst composition.

The aqueous solution containing the water-soluble titanium compound maybe obtained directly from commercial sources or may be made bydissolving the titanium compound in water. The concentration of theaqueous titanium solution can vary over a wide range. For example, thesolution can have a titanium compound concentration in the range of 25to 75 wt %, or 30 to 70 wt %, or 50 to 60 wt %.

The mode of adding the vanadium compound and the phosphorus compound tothe aqueous titanium solution is not particularly limiting. For example,the vanadium compound and the phosphorus compound may be blendedtogether to form a physical mixture or a reaction product, before beingadded to the aqueous titanium solution. Alternatively, the V and Pcompounds may be added sequentially in any order or simultaneously tothe aqueous titanium solution. Thus, as used herein, the expression“adding a vanadium compound and a phosphorus compound” can refer to theaddition of the vanadium compound and the phosphorus compound separatelyor collectively as a physical mixture or as a reaction product of thetwo.

Similarly, the heat-treating step and the water-removing step may beconducted sequentially or simultaneously. For example, in the case ofwater removal by distillation or evaporation, the heat-treating step cantake place during the distillation or evaporation.

The heat-treating step may be conducted over a wide temperature range,such as from above ambient up to 200° C. or higher. The purpose of theheat-treating step is to facilitate mixing and/or reaction among thecatalyst precursors. Depending on the catalyst precursors and thetemperature employed, the heat-treating step may be carried out fromseveral minutes to hours or days.

The water-removal step may be accomplished in a number of ways. Forexample, as mentioned above, water may be removed by distillation orevaporation. Alternatively, as discussed in more detail below, thecatalyst components can be precipitated out of solution by adding ananti-solvent to the mixture to precipitate out the catalyst componentsand separating the precipitate from the liquid to obtain the solidresidue. The water can then be removed by decanting or filtration.

Following the water-removal step, which may include a subsequent dryingstep, the resulting solid residue may be crushed and sieved to obtain adesired particle size. The sieved catalyst particles can then becalcined in one or more stages in air prior to use. The calciningtemperature is normally in the range of 200° C. to 800° C. Preferably,the calcining temperature ranges from 300° C. to 500° C. The calciningstep is typically carried out for 1 to 10 hours, and preferably for 2 to8 hours. Upon calcining, the mixed oxide catalyst according to theinvention is formed.

In addition to the water-soluble titanium compounds mentioned above, thecatalyst precursors may be ammonium salts, halides, oxyacids, oxyacidsalts, hydroxides, or oxides of vanadium, titanium, and phosphorus. Inone aspect of the invention the catalyst composition is prepared withthe organo-titanium compound comprising titanium(IV) bis(ammoniumlactate)dihydroxide.

The vanadium compound is preferably water soluble. Examples of suchcompounds include vanadium trichloride, vanadium(IV) sulfate oxidehydrate, and ammonium vanadate optionally treated with aqueous oxalicacid and/or lactic acid. Other water-soluble vanadium sources can alsobe used.

The phosphorus compound is also preferably water soluble. The compoundshould be converted to phosphorus oxides when calcined. Such phosphoruscompounds include phosphoric acid, phosphorous acid, and ammonium saltsof these acids.

A reducing compound can be added to the reaction mixture to impartadditional surface area to the resulting catalyst composition. Lacticacid is preferred for this purpose, but other compounds bearingbifunctional groups (i.e., bifunctional compounds) such as citric acid,glycolic acid, oxalic acid, ethylene glycol, butane diol, hexane diol,or pentane diol may also be used. Use of these surface area reagents isoptional, but is generally preferred. In one aspect of the invention,the bifunctional compound can be added to the mixture of catalystcomponents before the heat-treating step (c). In one aspect of theinvention, the bifunctional compound comprises lactic acid.

A practical example of a method for preparing the catalyst compositionaccording to the invention includes mixing a 50 wt % aqueous solution ofTBALDH with a solution of ammonium metavanadate and phosphoric acid inwater and, optionally, lactic acid; heating the mixture at 130° C. underagitation; removing water from the heat-treated mixture by distillation;and calcining the resulting residue at 300° C. and then at 450° C. inair.

Alternatively, according to another embodiment of the invention, thecatalyst composition may be prepared as described above except that awater-miscible non-solubilizing solvent, or “anti-solvent,” is added tothe reaction/heat-treating vessel to precipitate out the majority of thecatalyst components after the heat-treating step. In this way, energyintensive water removal by distillation can be avoided, and the catalystcomposition may instead be collected by filtration followed bycalcination. The anti-solvent may be polar compounds such as alcohols,ketones, aldehydes, ethers, or esters. Alcohols such as ethanol arepreferred as the anti-solvent.

The catalyst composition can have the general formula VTi_(a)P_(b)O_(c),wherein a=0.3 to 6.0, preferably 1.0 to 4.0; b=2.0 to 13.0, preferably4.0 to 10.0; and c is the number of atoms required to satisfy thevalences of the components other than oxygen.

The catalyst composition of the invention can be supported on an oxidesupport. Suitable oxide supports include silica, alumina, titaniumoxide, zirconium oxide, and titanium or zirconium pyrophosphates. Otheroxide supports may be used provided that they are inert to the desiredcatalytic reaction. The supports should be physically robust andpre-shaped. The term “pre-shaped” is used in this context to mean thatthe shape of the final catalyst is essentially the same as the startingsupport. The pre-shaped oxides typically can have average particlediameter sizes ranging from about 0.1 millimeter (mm) to about 20 mm.They can be in any common form such as extrudates, compressed pellets,or bulk solid that has been pulverized to the desired mesh size. Theymay also be in a variety of shapes such as rods, stars, cylinders,spheres, or broken chunks. Many of these oxide supports are availablecommercially, and their use simplifies the preparation of the catalystcomposition of the invention, although this is not a requirement of theinvention.

In supported embodiments, the titanium and the vanadium components canbe loaded onto the support separately or together. A preferred techniqueis to dissolve the desired amount of ammonium vanadate and oxalic acidor lactic acid in the aqueous TBALDH solution. This solution can bediluted if desired and then used to impregnate the oxide support usingthe incipient wetness technique. The impregnated support is then driedat about 110° C. The resulting material likely contains a homogeneousdispersion of the two metals since drying the solution at 110° C.produces a homogeneous glass. The dried support containing the vanadiumand titanium is then impregnated with the desired amount of the aqueoussolution of the phosphorus compound.

The order of impregnation normally is not critical. Excellent resultscan be obtained by co-impregnation with vanadium and titanium followedby impregnation with phosphorus after drying as illustrated above.

Excellent results can also be obtained using incipient wetnesstechniques for all of the impregnations. If a higher loading isrequired, more solution than required for incipient wetness can be usedfollowed by evaporation of the solvent. If desired, the solutions can beapplied to the outer regions of the oxide support.

After the vanadium, titanium, and phosphorus components have beenapplied to the support, the catalyst can be calcined, for example, atabout 450° C.

The ternary V—Ti—P catalyst composition disclosed herein is primarilyamorphous, as determined by x-ray diffraction analysis. Interestingly,the invention V—Ti—P catalyst composition prepared with TBALDH, forexample, produces acrylic acid in significantly higher yield (>20%) thanthe V—Ti—P material prepared with tetrachlorotitanium when a 55 weightpercent aqueous formaldehyde feed is used, even though both catalystsare amorphous materials. This result suggests that the microstructure orthe homogeneity of the invention catalyst is considerably different thanthat of the prior art catalyst.

In addition to higher yield, using a water-soluble titanium sourceoffers several advantages over using titanium chloride. For example, theformation of gaseous hydrochloric acid can be avoided; the discretetitanium(IV) precursor is a solute in water rather than a cumbersomeheterogeneous gel; and the resulting V—Ti—P catalyst is formed with aninherently higher specific surface area.

The propensity for a water-soluble titanium compound, such as TBALDH, toform an active V—Ti—P catalyst comes as a surprise, since titaniumsources other than TiCl₄ have been shown to produce inferior catalystsfor acrylic acid production. See, for example, M. Ai, Applied Catalysis,Vol. 48, pp. 51-61 (1989). For example, when titanium dioxide isemployed as a titanium precursor, the resulting material fails togenerate acrylic acid from formaldehyde and acetic acid. It has beenreported elsewhere that TiO₂ can form catalytically active materials foracrylate production (M. Abon et al., J. Catalysis, Vol. 156, pp. 28-36(1995)); however, this result could not be reproduced.

Also unexpected is the fact that exogenous lactic acid is no longerrequired in the catalyst synthesis, for example, when TBALDH is used.When lactic acid is omitted from the catalyst preparation involvingtetrachlorotitanium, the resulting material is highly crystalline, asdetermined by x-ray diffraction, but is relatively inactive towardacrylic acid synthesis. However, V—Ti—P materials prepared with TBALDH,for example, in the absence of lactic acid are amorphous and areconsiderably more active and selective. Avoiding lactic acid addition isappealing, since it minimizes the amount of steps in the catalystsynthesis and results in less organic material that must be combustedduring air calcination.

In a third aspect, the present invention provides a process forpreparing a 2,3-unsaturated carboxylic acid, such as acrylic acid ormethacrylic acid. Reference to “carboxylic acid” in this contextincludes the corresponding carboxylic acid ester, such as acrylate andmethacrylate.

The process of the invention comprises the step of contacting aformaldehyde source with a carboxylic acid in the presence of acondensation catalyst under vapor-phase condensation conditions toobtain the 2,3-unsaturated carboxylic acid. The condensation catalystcomprises a mixed oxide of vanadium (V), titanium (Ti), and phosphorus(P). The titanium component of the condensation catalyst is derived froma water-soluble, redox-active organo-titanium compound, as describedherein.

The 2,3-unsaturated carboxylic acid can be prepared with good yield,conversion, and selectivity. By “yield” it is meant the (moles ofproduct)/(moles of reactant fed)*100. For example, the % yield ofacrylic acid from formaldehyde is the (moles of acrylic acid)/(moles offormaldehyde fed)*100. By “conversion” it is meant the (moles ofreactant fed—moles of unreacted reactant)/(moles of reactant fed)*100.For example, the % formaldehyde conversion is (moles of formaldehydefed—moles of unreacted formaldehyde)/(moles of formaldehyde fed)*100. By“selectivity” it is meant (moles of product)/(moles of reactantfed—moles of unreacted reactant)*100. For example, % selectivity toacrylic acid from formaldehyde is (moles of acrylic acid)/(moles offormaldehyde fed—moles of unreacted formaldehyde)*100. One skilled inthe art recognizes that yield is also equal to conversion timesselectivity. When comparing examples, such as, Example B has an 80%formaldehyde conversion and Example C has a 60% formaldehyde conversion,the formaldehyde conversion of Example B is said to be 20% higher thanExample C. In other words, comparisons are simply the mathematicaldifference in the percentages from one example to another.

The formaldehyde source for use in the present invention is notparticularly limiting. It can be anhydrous formaldehyde itself,1,3,5-trioxane (sometimes referred to herein as simply “trioxane”),dimethoxymethane. Alternatively, the formaldehyde source may be anaqueous solution of formaldehyde. The aqueous formaldehyde solution cancontain, for example, from 30 to 65 weight percent formaldehyde.Examples of such solutions include formalin (37 wt % formaldehyde) andindustrial grade aqueous formaldehyde (55 wt % formaldehyde). Theaqueous formaldehyde solution may be obtained commercially, by oxidationof methanol, or by blending water with trioxane, for example, in a molarratio of approximately 4:1.

The carboxylic acid should have at least 2 hydrogen atoms in theposition alpha to the carboxylic acid group. The carboxylic acid ispreferably an aliphatic carboxylic acid having 2 to 4 carbon atoms.Acetic and propionic acids are preferred carboxylic acids. The mostpreferred carboxylic acid is acetic acid. The term “carboxylic acid” inthis context includes the corresponding carboxylic acid ester, whenformation of the 2,3-unsaturated carboxylic acid ester is desired.Examples of such carboxylic acid esters include acetate and propionate.

The description of the catalyst composition and the process for makingthe catalyst composition herein above, such as, for example, thedescription of vanadium, titanium, phosphorus, and alkali metalcompounds, the catalyst formula, the alkali metals, the pre-shapedsupports, the water removal step, and the bifunctional compound, applyto the process for preparing a 2,3-unsaturated carboxylic acid.

The molar ratio of the formaldehyde component to the carboxylic acidcomponent may be from 0.1 to 10, preferably from 0.2 to 5, and morepreferably from 0.2 to 2. The molar ratio of water to the formaldehydecomponent may be from 0 to 5, preferably from 0 to 3, and morepreferably from 0 to 1.5.

The process can be operated at a temperature from 200° C. to 400° C.,preferably from 225° C. to 375° C., and more preferably from 275° C. to375° C.

The process can be run at a pressure from 0.1 to 10 bars absolute(bara), preferably from 0.5 to 5 bara, and more preferably from 1 to 1.5bara.

In certain embodiments of the process of the invention, the liquid feedrate can range from 1.0 to 1000 mL/kg catalyst/minute, and preferablyfrom 10 to 100 mL/kg catalyst/minute.

In other embodiments of the process of the invention, the reactants canbe fed to the condensation reactor with oxygen along with an inertcarrier gas such as nitrogen or oxygen-depleted air. Gases recycled fromthe process can be used. The inert gas component can be present atconcentrations ranging from 0 to 90 mole % of the total feed, preferablyfrom 25 to 85 mole %, and more preferably from 30 to 80 mole %. Theconcentration of the oxygen component can range from 0.5 to 6 mole %,preferably from 2 to 5 mole %, and more preferably from 3 to 4 mole %.Low levels of oxygen allow for coke to build up on the catalyst. On theother hand, high levels of oxygen can lead to excessive combustion ofreactants and products.

In the oxygen co-feed embodiments, the space velocity should preferablyrange from 50 to 400 moles of feed/(kg catalyst-hr), more preferablyfrom 100 to 300 moles of feed/(kg catalyst-hr), and most preferably from125 and 200 moles of feed/(kg catalyst-hr). The term “moles of feed” ismeant to be inclusive of all of the species being fed to the catalystincluding organics, water, oxygen, and inerts. These embodiments of theinvention take advantage of the combined effects of feeding the correctlevels of oxygen, water, and elevated space velocity to increase rateand selectivity without significantly affecting the yield. Anydifferences in formaldehyde conversion are primarily the result offormaldehyde destruction when the space velocity is too low. In theevent of inhibitory coke formation, the catalyst may be regeneratedbetween reaction runs in air at, for example, 400° C.

Generally, increasing the space velocity of reactants increases the rateof a reaction, but this is normally accompanied with a correspondingdecrease in the yield and conversion. It has been unexpectedlydiscovered that certain conditions of the process can actually allow forincreased rate without a decrease in yield as the space velocity isincreased.

Inhibitors such as hydroquinone may be added to the 2,3-unsaturatedcarboxylic acid product to minimize polymerization.

In a fourth aspect, the present invention provides a process forpreparing a 2,3-unsaturated carboxylic acid. The process comprises thesteps of contacting a methylene dialkanoate and a diluent gas with acondensation catalyst under vapor-phase condensation conditions toobtain the 2,3-unsaturated carboxylic acid. The condensation catalystcomprises a mixed oxide of vanadium (V), titanium (Ti), and phosphorus(P). The methylene dialkanoate has the general formula (I):

wherein R is selected from the group consisting of hydrogen and an alkylgroup having 1 to 8 carbon atoms.

By “methylene dialkanoate,” it is meant that a —CH₂—, methylene group,is bonded to two alkanoate, carboxylate, groups. The alkanoate groupshould have at least 2 hydrogen atoms bonded to a carbon atom in theposition alpha to the carboxylate carbon. Acetate and propionate arepreferred alkanoates.

By “diluent gas,” it is meant a gas which is introduced so that this gasquantitatively lowers the concentration of the reactants in feed. Thecomposition of the “diluent gas” can be an inert carrier gas and/oroxygen; some examples of an inert gas include nitrogen, argon, oxygendepleted air, or air.

By “condensation catalyst,” it is meant a homogeneous or heterogeneouscatalyst that can combine reactant molecules with the concomitantelimination of water or other by-product molecules.

By “an alkyl group with 1 to 8 carbon atoms,” it is meant any saturatedhydrocarbon with 1 up to and including 8 carbons atoms. Some examples ofalkyl groups include methyl, ethyl, propyl, iso-propyl, butyl, isobutyl,tert-butyl, pentyl, hexyl, heptyl, and octyl.

The condensation catalyst comprises a mixed oxide of vanadium (V),titanium (Ti), and phosphorus (P). These catalysts can be made bymethods well known to one skilled in the art. The process can be carriedout using a catalyst having the general formula VTi_(a)P_(b)O_(c),wherein a=0.3 to 6.0, preferably 1.0 to 4.0; b=2.0 to 13.0, preferably4.0 to 10.0; and c is the number of atoms required to satisfy thevalences of the components other than oxygen.

In another aspect of the invention the VTi_(a)P_(b)O_(c), catalyst canbe the inventive catalyst wherein the titanium component is derived froma water-soluble, redox-active organo-titanium compound. Examples ofwater-soluble, redox-active organo-titanium compounds useful in theVTi_(a)P_(b)O_(c) catalyst include titanium lactates, titaniumalkanolamines, and titanium acetylacetonates. Such compounds arecommercially available, such as from Dorf Ketal under the trade nameTYZOR®. Practical examples of such compounds include titanium(IV)bis(ammonium lactate)dihydroxide (TBALDH), titanium diethanolamine,titanium triethanolamine, and titanium acetylacetonate. In one aspect,the organo-titanium compound comprises titanium(IV) bis(ammoniumlactate)dihydroxide.

The molar ratio of water to the methylene dialkanoate component may bebetween about 0 and 5, preferably between 0 and 1, and most preferablyat 0.

The process for preparing 2,3-unsaturated carboxylic acids can beoperated at a temperature between about 150° C. and 400° C., preferablybetween 200° C. and 375° C. and most preferably between 220° C. and 320°C. The process is normally operated at a pressure between about 0.1 and10 bars absolute (bara), preferably between 0.5 and 5 bara and mostpreferably between about 1 and 1.5 bara.

The process for preparing 2,3-unsaturated carboxylic acids can beperformed when the methylene dialkanoate is methylene dipropionate. Thisprocess can also be performed when the methylene dialkanoate ismethylene diacetate. Experiments performed with methylene diacetate ormethylene dipropionate produced no detectable paraformaldehyde in theprocess's reaction product and produced higher space time yields thanconventional feeds.

The methylene dialkanoate is contacted with the condensation catalyst inthe presence of a diluent gas. This diluent gas can be an inert carriergas and/or oxygen. Gases recycled from the process can be used. Thediluent gas component can be present at concentrations between 1 and 90mole percent based on the total moles of the methylene dialkanoate anddiluent gas, preferably between about 25 and 75 mole percent, and mostpreferably between about 30 and 65 mole percent.

The oxygen concentration can be between about 0.5 to 20 mole based onthe total moles of diluent gas, preferably between 2 and 10 mole %, andmost preferably between about 4 and 6 mole %. Low levels of oxygen allowfor coke to build up on the catalyst. High levels of oxygen can lead toexcessive combustion of reactants and products.

The space time yield is preferably between about 0.1 and 200 moles of2,3 unsaturated carboxylic acid/(kg catalyst-hr), more preferablybetween about 1 and 50 moles of 2,3 unsaturated carboxylic acid/(kgcatalyst-hr) and most preferably between about 2 and 10 moles of 2,3unsaturated carboxylic acid/(kg catalyst-hr). In the event of inhibitorycoke formation, the catalyst may be regenerated between reaction runs inair at 400° C.

In a fifth aspect, the present invention provides a process forpreparing a 2,3-unsaturated carboxylic acid. The process comprises thestep of contacting a methylene dial kanoate and diluent gas with acondensation catalyst under vapor-phase condensation conditions toobtain the 2,3-unsaturated carboxylic acid. The condensation catalystcomprises a mixed oxide of vanadium (V), titanium (Ti), and phosphorus(P). The titanium component is derived from a water-soluble,redox-active organo-titanium compound. The methylene dialkanoate has thegeneral formula (I):

wherein R is selected from the group consisting of hydrogen, methyl,ethyl, propyl, and isopropyl.

The description of the catalyst composition, the process for making theinventive catalyst composition, and the processes for preparing a2,3-unsaturated carboxylic acid herein above, such as, for example, thedescription of vanadium, titanium, phosphorus, and alkali metalcompounds, the catalyst formula, the alkali metals, the pre-shapedsupports, the water removal step, and the bifunctional compound, applyto the process for preparing a 2,3-unsaturated carboxylic acid.

For example, the process can be carried out using a catalyst having thegeneral formula VTi_(a)P_(b)O_(c), wherein a=0.3 to 6.0, preferably 1.0to 4.0; b=2.0 to 13.0, preferably 4.0 to 10.0; and c is the number ofatoms required to satisfy the valences of the components other thanoxygen.

Examples of water-soluble, redox-active organo-titanium compounds usefulin the VTi_(a)P_(b)O_(c) catalyst include titanium lactates, titaniumalkanolamines, and titanium acetylacetonates. Such compounds arecommercially available, such as from Dorf Ketal under the trade nameTYZOR®. Practical examples of such compounds include titanium(IV)bis(ammonium lactate)dihydroxide (TBALDH), titanium diethanolamine,titanium triethanolamine, and titanium acetylacetonate. In one aspect,the organo-titanium compound comprises titanium(IV) bis(ammoniumlactate)dihydroxide.

The molar ratio of water to the methylene dialkanoate component may bebetween about 0 and 5, preferably between 0 and 1, and most preferablyat 0.

The process for preparing 2,3-unsaturated carboxylic acids can beoperated at a temperature between about 150° C. and 400° C., preferablybetween 200° C. and 375° C. and most preferably between 220° C. and 320°C. The process is normally operated at a pressure between about 0.1 and10 bars absolute (bara), preferably between 0.5 and 5 bara and mostpreferably between about 1 and 1.5 bara.

The process for preparing 2,3-unsaturated carboxylic acids can beperformed when the methylene dialkanoate is methylene dipropionate. Thisprocess can also be performed when the methylene dialkanoate ismethylene diacetate. Experiments performed with methylene diacetate ormethylene dipropionate produced no detectable paraformaldehyde in theprocess's reaction product and produced higher space time yields thancomparable conventional feeds.

The methylene dialkanoate is fed with a diluent gas to achieve contactwith the condensation catalyst. This diluent gas can be an inert carriergas and/or oxygen. Gases recycled from the process can be used. Thediluent gas component can be present at concentrations between 1 and 90mole percent based on the total moles of the methylene dialkanoate anddiluent gas, preferably between about 25 and 75 mole percent, and mostpreferably between about 30 and 65 mole percent.

The oxygen concentration can be between about 0.5 to 20 mole % based onthe total moles of diluent gas, preferably between 2 and 10 mole %, andmost preferably between about 4 and 6 mole %. Low levels of oxygen allowfor coke to build up on the catalyst. High levels of oxygen can lead toexcessive combustion of reactants and products.

The space time yield should preferably range between about 0.1 and 200moles of 2,3 unsaturated carboxylic acid/(kg catalyst-hr), morepreferably between about 1 and 50 moles of 2,3 unsaturated carboxylicacid/(kg catalyst-hr) and most preferably between about 2 and 10 molesof 2,3 unsaturated carboxylic acid/(kg catalyst-hr). In the event ofinhibitory coke formation, the catalyst may be regenerated betweenreaction runs in air at 400° C.

Listing of Non-Limiting Embodiments

Embodiment A is a catalyst composition comprising a mixed oxide ofvanadium (V), titanium (Ti), and phosphorus (P), wherein the titaniumcomponent is derived from a water-soluble, redox-active organo-titaniumcompound.

The catalyst composition of Embodiment A which has the general formulaVTi_(a)P_(b)O_(c), wherein a is a number from 0.3 to 6.0, b is a numberfrom 2.0 to 13.0, and c is the number of atoms required to satisfy thevalences of V, Ti, and P; or wherein a ranges from 1.0 to 4.0 and branges from 4.0 to 10.0.

The catalyst composition of Embodiment A or Embodiment A with one ormore of the intervening features wherein the organo-titanium compoundcomprises titanium(IV) bis(ammonium lactate)dihydroxide.

The catalyst composition of Embodiment A or Embodiment A with one ormore of the intervening features which further comprises a pre-shapedsupport.

The catalyst composition of Embodiment A or Embodiment A with one ormore of the intervening features which further comprises a pre-shapedsupport, wherein the pre-shaped support comprises silica, alumina,titanium oxide, titanium pyrophosphate, zirconium oxide, or zirconiumpyrophosphate.

The catalyst composition of Embodiment A or Embodiment A with one ormore of the intervening features which further comprises a pre-shapedsupport, wherein the pre-shaped support has a particle size ranging from0.1 mm to 20 mm.

Embodiment B is a method for preparing a catalyst composition comprisinga mixed oxide of vanadium (V), titanium (Ti), and phosphorus (P). Themethod comprises the steps of:

-   -   (k) providing an aqueous solution comprising a water-soluble,        redox-active organo-titanium compound;    -   (l) adding a vanadium compound and a phosphorus compound to the        aqueous titanium solution to form a mixture of catalyst        components;    -   (m) heat-treating the mixture;    -   (n) removing water from the heat-treated mixture to obtain a        solid residue comprising the catalyst components; and    -   (o) calcining the solid residue at an elevated temperature in        the presence of air to obtain the catalyst composition.

The method of Embodiment B wherein the water removing step (d) comprisesdistillation or evaporation.

The method of Embodiment B wherein the water removing step (d) comprisesadding an anti-solvent to the mixture to precipitate out the catalystcomponents and separating the precipitate from the liquid to obtain thesolid residue.

The method of Embodiment B wherein the water removing step (d) comprisesadding an anti-solvent to the mixture to precipitate out the catalystcomponents and separating the precipitate from the liquid to obtain thesolid residue, and wherein the precipitate is separated from the liquidby filtration.

The method of Embodiment B wherein the water removing step (d) comprisesadding an anti-solvent to the mixture to precipitate out the catalystcomponents and separating the precipitate from the liquid to obtain thesolid residue, wherein the precipitate is separated from the liquid byfiltration, and wherein the anti-solvent is a polar compound selectedfrom alcohols, ketones, aldehydes, ethers, and esters; or wherein theanti-solvent is an alcohol.

The method of Embodiment B or Embodiment B with one or more of theintervening features wherein the catalyst composition has the generalformula VTi_(a)P_(b)O_(c), wherein a is a number from 0.3 to 6.0, b is anumber from 2.0 to 13.0, and c is the number of atoms required tosatisfy the valences of V, Ti, and P; or wherein a ranges from 1.0 to4.0, and b ranges from 4.0 to 10.0.

The method of Embodiment B or Embodiment B with one or more of theintervening features wherein the organo-titanium compound comprisestitanium(IV) bis(ammonium lactate)dihydroxide.

The method of Embodiment B or Embodiment B with one or more of theintervening features wherein the catalyst composition further comprisesa pre-shaped support.

The method of Embodiment B or Embodiment B with one or more of theintervening features which further comprises a pre-shaped support,wherein the pre-shaped support comprises silica, alumina, titaniumoxide, titanium pyrophosphate, zirconium oxide, or zirconiumpyrophosphate.

The method of Embodiment B or Embodiment B with one or more of theintervening features which further comprises a pre-shaped support,wherein the pre-shaped support has a particle size ranging from 0.1 mmto 20 mm.

The method of Embodiment B or Embodiment B with one or more of theintervening features wherein the catalyst composition further comprisesa pre-shaped support, and wherein the pre-shaped support is added to themixture of catalyst components before the heat-treating step (c).

The method of Embodiment B or Embodiment B with one or more of theintervening features which further comprises adding a bifunctionalcompound to the mixture of catalyst components before the heat-treatingstep (c), wherein the bifunctional compound comprises citric acid,lactic acid, glycolic acid, oxalic acid, ethylene glycol, butane diol,pentane diol, or hexane diol; or wherein the bifunctional compoundcomprises lactic acid.

Embodiment C is a process for preparing a 2,3-unsaturated carboxylicacid. The process comprises the step of contacting a formaldehyde sourcewith a carboxylic acid in the presence of a condensation catalyst undervapor-phase condensation conditions to obtain the 2,3-unsaturatedcarboxylic acid. The condensation catalyst comprises a mixed oxide ofvanadium (V), titanium (Ti), and phosphorus (P). The titanium componentof the condensation catalyst is derived from a water-soluble,redox-active organo-titanium compound.

The process of Embodiment C wherein the formaldehyde source comprisesformaldehyde, 1,3,5-trioxane, or dimethoxymethane, and the carboxylicacid comprises acetic acid or propionic acid.

The process of Embodiment C or Embodiment C with one or more of theintervening features wherein the formaldehyde source comprises anaqueous solution of formaldehyde, 1,3,5-trioxane, or dimethoxymethane,and the carboxylic acid comprises acetic acid or propionic acid.

The process of Embodiment C or Embodiment C with one or more of theintervening features wherein the formaldehyde source comprises anaqueous solution of formaldehyde, 1,3,5-trioxane, or dimethoxymethane,and the carboxylic acid comprises acetic acid or propionic acid, andwherein the aqueous solution comprises from 30 to 65 weight percentformaldehyde.

The process of Embodiment C or Embodiment C with one or more of theintervening features wherein the organo-titanium compound comprisestitanium(IV) bis(ammonium lactate)dihydroxide.

The process of Embodiment C or Embodiment C with one or more of theintervening features wherein the catalyst composition further comprisesa pre-shaped support.

The process of Embodiment C or Embodiment C with one or more of theintervening features which further comprises a pre-shaped support,wherein the pre-shaped support comprises silica, alumina, titaniumoxide, titanium pyrophosphate, zirconium oxide, or zirconiumpyrophosphate.

The process of Embodiment C or Embodiment C with one or more of theintervening features which further comprises a pre-shaped support,wherein the pre-shaped support has a particle size ranging from 0.1 mmto 20 mm.

The process of Embodiment C or Embodiment C with one or more of theintervening features wherein the condensation conditions comprise atotal feed space velocity of 50 to 400 moles of feed/(kg catalyst•hr);or the total feed space velocity ranges from 100 to 300 moles offeed/(kg catalyst•hr); or the total feed space velocity ranges from 125to 200 moles of feed/(kg catalyst•hr).

This invention can be further illustrated by the following workingexamples, although it will be understood that these examples areincluded merely for purposes of illustration and are not intended tolimit the scope of the invention. Unless otherwise indicated or thecontext indicates otherwise, all percentages are by weight.

Embodiment D is a process for preparing a 2,3-unsaturated carboxylicacid. The process comprises the step of contacting a methylenedialkanoate and a diluent gas with a condensation catalyst undervapor-phase condensation conditions to obtain the 2,3-unsaturatedcarboxylic acid. The condensation catalyst comprises a mixed oxide ofvanadium (V), titanium (Ti), and phosphorus (P). The methylenedialkanoate has the general formula (I):

wherein the R is selected from the group consisting of hydrogen and analkyl group having 1 to 8 carbons.

The process of Embodiment D wherein the condensation catalyst has theformula VTi_(a)P_(b)O_(c), wherein a is a number from 0.3 to 6.0, b is anumber from 2.0 to 13.0, and c is the number of atoms required tosatisfy the valences of the components other than oxygen.

The process of Embodiment D or Embodiment D with one or more of theintervening features wherein the titanium component is derived from awater-soluble, redox-active organo-titanium compound.

The process of Embodiment D or Embodiment D with one or more of theintervening features wherein the organo-titanium compound comprisestitanium(IV) bis(ammonium lactate)dihydroxide.

The process of Embodiment D or Embodiment D with one or more of theintervening features wherein the methylene dialkanoate is methylenedipropionate.

The process of Embodiment D or Embodiment D with one or more of theintervening features wherein the methylene dialkanoate is methylenediacetate.

The process of Embodiment D or Embodiment D with one or more of theintervening features wherein the contacting occurs with 1 mol % to 90mole % diluent gases, based on the total moles of the methylenedialkanoate and the diluent gas.

The process of Embodiment D or Embodiment D with one or more of theintervening features wherein the diluent gas comprises from about 0.5mole % to about 20 mole % oxygen, based on the total moles of diluentgas.

The process of Embodiment D or Embodiment D with one or more of theintervening features wherein the space time yield of the 2,3 unsaturatedcarboxylic acid is from about 0.1 and 200 moles of 2,3 unsaturatedcarboxylic acid/(kg catalyst-hr), more preferably between about 1 and 50moles of 2,3 unsaturated carboxylic acid/(kg catalyst-hr) and mostpreferably between about 2 and 10 moles of 2,3 unsaturated carboxylicacid/(kg catalyst-hr).

The process of Embodiment D or Embodiment D with one or more of theintervening features wherein the catalyst composition further comprisesa pre-shaped support.

The process of Embodiment D or Embodiment D with one or more of theintervening features which further comprises a pre-shaped support,wherein the pre-shaped support comprises silica, alumina, titaniumoxide, titanium pyrophosphate, zirconium oxide, or zirconiumpyrophosphate.

The process of Embodiment D or Embodiment D with one or more of theintervening features which further comprises a pre-shaped support,wherein the pre-shaped support has a particle size ranging from 0.1 mmto 20 mm.

Embodiment E is a process for preparing a 2,3-unsaturated carboxylicacid. The process comprises the step of contacting a methylenedialkanoate and a diluent gas with a condensation catalyst undervapor-phase condensation conditions to obtain the 2,3-unsaturatedcarboxylic acid. The condensation catalyst comprises a mixed oxide ofvanadium (V), titanium (Ti), and phosphorus (P). The titanium componentis derived from a water-soluble, redox-active organo-titanium compound.The methylene dialkanoate has the general formula (I):

wherein the R is selected from the group consisting of hydrogen, methyl,ethyl, propyl, and isopropyl.

The process of Embodiment E wherein the organo-titanium compoundcomprises titanium(IV) bis(ammonium lactate)dihydroxide.

The process of Embodiment E or Embodiment E with one or more of theintervening features wherein the condensation catalyst has the formulaVTi_(a)P_(b)O_(c), wherein a is a number from 0.3 to 6.0, b is a numberfrom 2.0 to 13.0, and c is the number of atoms required to satisfy thevalences of the components other than oxygen.

The process of Embodiment E or Embodiment E with one or more of theintervening features wherein the methylene dialkanoate is methylenedipropionate.

The process of Embodiment E or Embodiment E with one or more of theintervening features wherein the methylene dialkanoate is methylenediacetate.

The process of Embodiment E or Embodiment E with one or more of theintervening features wherein the contacting occurs with between 1 and 90mole percent based on the total moles of the methylene dialkanoate anddiluent gas, preferably between about 25 and 75 mole percent, and mostpreferably between about 30 and 65 mole percent.

The process of Embodiment E or Embodiment E with one or more of theintervening features wherein the diluent gas comprises from about 0.5 to20 mole % oxygen, based on the total moles of diluent gas, preferablybetween 2 and 10 mole %, and most preferably between about 4 and 6 mole%.

The process of Embodiment E or Embodiment E with one or more of theintervening features wherein the space time yield of the 2,3 unsaturatedcarboxylic acid is from about 0.1 and 200 moles of 2,3 unsaturatedcarboxylic acid/(kg catalyst-hr), more preferably between about 1 and 50moles of 2,3 unsaturated carboxylic acid/(kg catalyst-hr) and mostpreferably between about 2 and 10 moles of 2,3 unsaturated carboxylicacid/(kg catalyst-hr).

The process of Embodiment E or Embodiment E with one or more of theintervening features wherein the catalyst composition further comprisesa pre-shaped support.

The process of Embodiment E or Embodiment E with one or more of theintervening features which further comprises a pre-shaped support,wherein the pre-shaped support comprises silica, alumina, titaniumoxide, titanium pyrophosphate, zirconium oxide, or zirconiumpyrophosphate.

The process of Embodiment E or Embodiment E with one or more of theintervening features which further comprises a pre-shaped support,wherein the pre-shaped support has a particle size ranging from 0.1 mmto 20 mm.

EXAMPLES Materials

D/L-Lactic acid (90 wt %), ammonium metavanadate (99+wt % NH₄VO₃),phosphoric acid (85 wt % H₃PO₄), titanium(IV) bis(ammoniumlactate)dihydroxide (50 wt % solution in water), tetrachlorotitanium(≧99 wt % TiCl₄), and titanium dioxide colloidal suspension in water(23.38 wt % TiO₂) were purchased from commercial suppliers and used asreceived.

Abbreviations

XRD=Powder X-ray Diffraction, XRF=X-ray Fluorescence Spectroscopy,TPD=Temperature Programmed Desorption, SCCM=standard cubic centimetersper minute; MeOAc=methyl acetate, MeOH=methanol, MA=methyl acrylate,H2CO=formaldehyde, HOAc=acetic acid, HOPr=propionic acid,mmol=millimoles, prod=product, AA=acrylic acid,BSTFA=N,O-bis(trimethylsilyl)trifluoroacetamide, andTMSCl=trimethylsilyl chloride.

XRD Measurements

All XRD measurements were performed on a Rigaku Miniflex X-RayDiffraction Spectrometer using a Copper anode X-Ray tube operated at 30kV and 15 mA. Diffraction patterns were collected from 5 degree twotheta angle to 75 degree two theta angle with a sampling width of 0.02degrees and a scan speed of 1.00 degrees/min.

Crystallite size was calculated based on the measurement of the fullwidth half maximum for peaks in the diffraction pattern and use of theScherrer equation (P. N. Scherrer, Ges. Wiss. Gottingen, Math.—Phys. KI.2, 96-100 (1918)). Quantitative phase analysis was calculated using arefinement algorithm base on the Rietveld method (H. M. Rietveld, J.Applied Crystallography 21, 86-91 (1988)). Percent crystallinity wascalculated based on integrated intensities from the individualdiffraction patterns with peaks of crystallite size greater than 30 Ådefined as crystalline and peaks of crystallite size less than or equalto 30 Å defined as amorphous (N. S. Murthy et al., Polymers 31, 996-1002(1990)).

Temperature Desorption Measurements

TPD determinations were conducted using a Mass Spectrometer attached tothe outlet of a Micrometrics Autochem II 2920 analyzer. Thedetermination of total acidity and total basicity using isopropanol asthe probe molecule is performed as follows. Approximately 0.05 grams ofsample is weighed into a quartz U tube which is placed in a ceramicfurnace. The sample is subjected to a programmed temperature cycle thatconsists of a heat cycle to 450° C. under 10% oxygen in Helium, acooling step to 40° C. Isopropanol is dosed on the sample using thevapor generator of the Micromeritics Autochem 2920 Analyzer. The vaporgenerator operates by bubbling helium through a flask containingisopropanol at room temperature. The resulting “vapor-saturated” heliumis transferred through a heated sample loop and injected over thesample. After saturating the surface of the sample, dry helium is passedover the sample to remove any physisorbed vapor. Then a final heating to˜450° C. at 20° C./min in a flowing stream of He at which time massspectral data is collected from the gas flowing through the sample.

Gas Chromatography Measurements

Liquid product samples were collected over a measured time period,weighed, and analyzed by gas chromatography. Samples were weighed into agas chromatography (GC) vial to a recorded weight of 0.1XXX (where X isthe actual number shown on the balance). Then, a LEAP unit was used torobotically add 200 μL of internal standard (0.7325 g dodecane in 100 mLpyridine), followed by 1.0 mL of BSTFA (w/TMSCl). The vials were thenplaced on a heat plate at 80° C. for 30 minutes. To separate allcomponents, each sample was injected on two columns running in parallelon one instrument, a Shimadzu 2010 gas chromatograph with an AOC-20autosampler. Gas Chromatography measurements were used to quantify allcomponents in the liquid product except formaldehyde.

Liquid Chromatography Measurements.

Quantitation of formaldehyde in the liquid product was performed usinghigh performance liquid chromatography after reaction mixture sampleswere subjected to acid hydrolysis in aqueous 25% v/v H₂SO₄ at 80° C. for30 minutes. The acid hydrolysate was reacted with dinitrophenylhydrazinethen analyzed using a Phenomenex Luna C8 column using a 1:1water:acetonitrile mobile phase under isocratic conditions. Separationand detection of the 2,4-dinitrophenylhydrazone derivative offormaldehyde was carried out using an Agilent 1100 HPLC system with aUV-Vis Detector monitoring at 360 nm. The formaldehyde concentration inthe liquid product was calculated based on calibration using externalstandards prepared from formalin. Quantitation of formaldehyde in theliquid feed was calculated based upon the ratio of water to trioxane andthe liquid feed flow rate.

Example 1 Preparation of an Amorphous V—Ti—P Catalyst Via Method a andReactor Screening with an Anhydrous Liquid Feed 1. Preparation of V(IV)H₃PO₄ Solution

The orange-beige ammonium metavanadate (9.75 g) was suspended in 50 mLof lactic acid and 200 mL of deionized water in a 500-mL single-neckedround-bottomed flask. After heating at 70° C. for 1 hour, 85%orthophosphoric acid (52.5 g) was added to the clear blue vanadiumsolution at 70° C. over a 15-minute period to give a blue-greensolution. Residual reactants were washed into the reaction flask with aminimal amount of water.

2. Preparation of V—Ti—P Catalyst

The 50 wt % titanium(IV) bis(ammonium lactate)dihydroxide solution(109.19 g) was added to a 1-L three-necked kettle reactor equipped witha condenser and a mechanical stirrer. The V/P solution from step 1 abovewas slowly poured into the Ti solution to give a blue suspension. TheV/P flask was rinsed with 30 mL of water and the contents were added tothe reaction flask. The mixture was then stirred at 700 to 800 rpm at130° C. for 16 hours to give a blue to blue-green suspension. The waterwas then removed via distillation over 4 to 6 h (oil bath set at 130°C.), and the resulting damp pale green solid was transferred to aceramic dish and heated in air at 300° C. for 16 hours in a mufflefurnace. The resulting solid was then crushed and sieved through an 8×14mesh. The 8×14 meshed material was then calcined for 6 hours at 450° C.in air (60 SCCM) in a quartz tube furnace to give pale green irregularlyshaped pellets. The surface properties and bulk composition of thecatalyst prepared in this example are summarized in Table 1.

3. Preparation of Acrylic Acid

The vapor-phase condensation experiment with molar ratio 12 aceticacid/1 trioxane feed was performed at 325° C., 0.083 mL liquidfeed/minute, and 80 SCCM N₂ for three hours. The performance of thecatalyst is summarized in Table 3. In Table 3, the term “Product, g”refers to the mass of the liquid products recovered. The term “Reactantsfed, g” includes only those reactants fed as liquids to the reactor:trioxane and acetic acid.

The condensation reaction of acetic acid and trioxane (the formaldehydesource) was performed in a 25-mm outer diameter (21 mm inner diameter)quartz reactor tube with length=61 cm (24 inches). Heat to the reactorwas provided by a Barnstead International electric tube furnace (typeF21100). Liquid products were collected in a three-necked flask fittedto a water-cooled condenser, which was attached to a dry-ice condenserwith a trap. The third neck of the flask was fitted with a stopper whichallowed for the addition of a few crystals of hydroquinone inhibitor.Hydroquinone crystals were added at the beginning of the collection ofeach sample. The base of the receiver flask was fitted with a stopcockto allow for draining of the liquid products.

The quartz reactor had indentations 20 cm (8 inches) up from the base ofthe tube. The region of the reactor with the indentations was situatednear the base of the heated section of the furnace. The reactor was alsofitted with a thermowell that extended from the top of the reactor toabout an inch below the indentations. The reactor was first loaded withquartz chips to about 2.5 inches in height above the indentations toallow the catalyst to be positioned in the middle of the furnace. Thereactor was then loaded with a 5.0 g charge of catalyst. Thethermocouple in the thermowell was placed near the center of thecatalyst bed. Sufficient quartz chips (about 2.5 inches) were added tothe region above the catalyst charge to reach the top of the heatedregion of the furnace. The performance of this catalyst is summarized inTable 3.

This example illustrates that the TBALDH compound is a suitableprecursor for the synthesis of a catalytically active V—Ti—P material,providing acrylic acid in good yield and in high purity under standardscreening conditions. The molar composition of the catalyst was nearlyidentical to that of the catalyst used in Comparative Example 1 below,however the catalyst in Comparative Example 1 has only 60% of thesurface area compared to the catalyst of Example 1. The total acid siteswere higher for the catalyst of Example 1 as compared to the catalyst ofComparative Example 1; 92.5 (μmol/g) compared to 64.2 (μmol/g),respectively. Powder x-ray diffraction analysis of the catalyst revealsthat it is primarily amorphous (FIG. 1).

Comparative Example 1 Preparation of an Amorphous V—Ti—P Catalyst ViaMethod B and Reactor Screening with an Anhydrous Liquid Feed

The catalyst in this example was prepared according to the methodsdescribed in M. Ai, Applied Catalysis, Vol. 48, pp. 51-61 (1989) and JP1989-068335A.

1. Ti(OH)₄ gel Preparation

A 5-L three-necked round bottomed flask was charged with 300 mL of waterice and 300 mL of deionized water. The flask was fitted with a 125-mLaddition funnel and vented to an aqueous saturated sodium bicarbonatesolution. Tetrachlorotitanium (34.6 g) was then added slowly to thevigorously stirred water/ice mix. The reactor atmosphere was flushedinto the scrubber solution with an air flow to remove gaseous HCl. ThepH of the resulting colorless solution was between 0 and 1.

Once the solution warmed to room temperature, it was diluted with 2.5 Lof deionized water and the pH was adjusted to between 10 and 11 by theaddition of 200 mL of 5.0 M ammonium hydroxide. A bright white solidformed immediately. This material was filtered and washed with 2×1 L ofwater to give white pieces of a paste-like substance, which was airdried for up to five hours to give a white material with a gel-likeconsistency.

2. Preparation of V(IV) H₃PO₄ Solution

A V/P solution was prepared following the procedure of Example 1, step1.

3. Preparation of V—Ti—P Catalyst

The hydroxide gel from step 1 above was suspended in 200 mL of water ina 1-L three-necked kettle reactor equipped with a condenser andmechanically stirred at 700 to 800 rpm long enough to obtain ahomogeneous white suspension. The V/P solution from step 2 above wasslowly poured into the gel suspension to give a blue suspension. The V/Pflask was rinsed with 50 mL of water and the contents were added to thereaction flask. The mixture was then stirred at 700 to 800 rpm at 130°C. for 16 hours to give a blue to blue-green suspension.

The water was then removed via distillation over 6 h (oil bath set at130° C.) and the resulting damp pale green solid was transferred to aceramic dish and heated in air at 300° C. for 16 hours in a mufflefurnace. The resulting solid was then crushed and sieved through an 8×14mesh. The 8×14 meshed material was then calcined for 6 hours at 450° C.in air (60 SCCM) in a quartz tube furnace to give pale green irregularlyshaped pellets. The surface properties and bulk composition of thecatalyst prepared in this example are summarized in Table 1. Powderx-ray diffraction analysis of the catalyst reveals that it is primarilyamorphous (FIG. 2).

4. Preparation of Acrylic Acid

The condensation reaction of acetic acid and trioxane (the formaldehydesource) in this example was performed as described in Example 1 exceptthat a 25-mm outer diameter (21 mm inner diameter) quartz reactor tubewith length=107 cm (42 inches) was used. Heat to the reactor wasprovided by a Lindberg 3-element electric furnace having a heated zone61 cm (24 inches) in length. Liquid products were collected in athree-necked flask fitted to a water cooled condenser, which wasattached to a dry ice condenser with a trap. The third neck of the flaskwas fitted with a stopper which allowed for the addition of a fewcrystals of hydroquinone inhibitor. Hydroquinone crystals were added atthe beginning of the collection of each sample. The base of the receiverflask was fitted with a stopcock to allow for draining of the liquidproducts. Liquid samples were collected over a measured time period,weighed, and analyzed by gas chromatography.

The quartz reactor had indentations 30.5 cm (12 inches) up from the baseof the tube. The region of the reactor with the indentations wassituated near the base of the heated section of the furnace. The reactorwas also fitted with a thermowell that extended from the top of thereactor to about an inch below the indentations. The reactor was firstloaded with quartz chips to about 10 inches in height above theindentations to allow the catalyst to be positioned in the middle of the3-element furnace. The reactor was then loaded with a 5.0 g charge ofcatalyst. The thermocouple in the thermowell was placed 1.5 inches upfrom the base of the catalyst bed. Sufficient quartz chips were added tothe region above the catalyst charge to reach the top of the heatedregion of the 3-element furnace. The performance of the catalyst issummarized in Table 3.

This example demonstrates that the preparation method according to theprior art was reproducible and that the resulting catalyst performedsimilarly to the invention catalyst described in Example 1. Under aninert atmosphere and using an anhydrous liquid feed, both catalystsproduced acrylic acid in good yield. The acetic acid accountability wasnearly identical in both cases. Both catalysts were also amorphous andhad a similar bulk composition. Despite these superficial similarities,the microstructure of the catalysts in this example and Example 1differed considerably as evidenced by the contrast in surface area andacidity measurements.

Comparative Example 2 Preparation of a Mixed Crystalline-AmorphousV—Ti—P Catalyst via Method C and Reactor Screening with an AnhydrousLiquid Feed 1. Preparation of V(IV) H₃PO₄ Solution

A V/P solution was prepared following the procedure of Example 1, step1.

2. Preparation of V—Ti—P Catalyst

A 23.38 wt % titanium dioxide colloidal dispersion (41.3 g) and 100 mLof deionized water were added to a 1-L three-necked kettle reactorequipped with a condenser and a mechanical stirrer. The V/P solutionfrom step 1 above was slowly poured into the suspension to give a bluesuspension. The V/P flask was rinsed with 25 mL of water and thecontents were added to the reaction flask. The mixture was then stirredat 700 to 800 rpm at 130° C. for 16 hours to give a blue-greensuspension. The water was then removed via distillation over 6 h (oilbath set at 130° C.) and the resulting damp pale green solid wastransferred to a ceramic dish and heated in air at 300° C. for 16 hoursin a muffle furnace. The resulting solid was then crushed and sievedthrough an 8×14 mesh. The 8×14 meshed material was then calcined for 6hours at 450° C. in air (60 SCCM) in a quartz tube furnace to give darkgrey irregularly shaped pellets. The surface properties and bulkcomposition of the catalyst prepared in this example are summarized inTable 1. The vapor-phase condensation experiment and the productanalysis were carried out as described in Example 1. The performance ofthe catalyst is summarized in Table 3.

This example illustrates that titanium dioxide is an unsuitableprecursor for preparing a catalytically active V—Ti—P catalyst. Notably,the BET surface area was comparatively low, as were the total acid sitesand the overall bulk molar composition, relative to vanadium. Thismaterial failed to generate acrylic acid from formaldehyde and aceticacid. Powder x-ray diffraction analysis of the catalyst revealed that itis a mixture of an unknown amorphous material and crystalline rutile(FIG. 3).

Comparative Example 3 Preparation of a Crystalline VO(HPO₄)(H₂O)_(0.5)Catalyst Method D and Reactor Screening with an Anhydrous Liquid Feed

The catalyst in this example was prepared according to the proceduredescribed in J. K. Bartley et al., “Vanadium Phosphate Catalysts,” MetalOxide Catalysis, pp. 499-537 (S. D. Jackson & J. S. J Hargreaves eds.2009).

A 1-L kettle reactor equipped with a mechanical stirrer, a condenser,and an addition funnel was charged with 100.08 g of vanadium pentoxideand 600 mL of isobutyl alcohol all under a nitrogen atmosphere. Thecontents were heated at reflux (oil bath set at 130° C.) for 1 hour,then 139.44 g of 85% phosphoric acid was added slowly, and the reactiontemperature was maintained at reflux for 22 hours. The resulting skyblue suspension contained small amounts of dark insoluble materials.Another 5.53 g of 85% phosphoric acid was then added along with anadditional 150 mL of iso-butanol. The reflux was then continued foranother seven hours. Upon cooling to room temperature, the bluesuspension was poured on to a Buchner funnel with filter paper; theheavier insoluble impurities remained in the reaction flask. The bluesolid was then isolated by vacuum filtration and washed with 200 mL ofethanol and dried at room temperature while pulling a vacuum. Watersoluble impurities were removed by heating a suspension of the bluesolid in water to reflux overnight under a nitrogen atmosphere. Themixture was then filtered while still hot, leaving a blue solid on thefilter paper and a yellow filtrate in the filter flask. The blue solidwas then dried at 110° C. for 22 hours in air to give a blue-green cake.This material was then crushed and sieved through an 8×14 mesh. XRDanalysis of this material (FIG. 4) showed it to be crystallineVO(HPO₄)(H₂O)_(0.5). The surface properties and bulk composition of thecatalyst prepared in this example are summarized in Table 1. Thevapor-phase condensation experiment was carried out according to thedescription in Example 1. The performance of the catalyst is summarizedin Table 4.

This example demonstrates that the catalyst prepared via Method D wasnot as effective at producing acrylic acid as the invention V—Ti—Pcatalyst in Example 1 or the V—Ti—P catalyst in Comparative Example 1.As depicted in the XRD pattern, the surface of this catalyst wascomposed of crystalline vanadyl hydrogen phosphate hemihydrate. Thisdiscrete species was not observed from similar XRD analysis of theamorphous catalysts described in either Example 1 or Comparative Example1.

Comparative Example 4 Preparation of a Crystalline (VO)₂(P₂O₇) Catalystvia Method E and Reactor Screening with an Anhydrous Liquid Feed

The catalyst in this example was prepared according to the proceduredescribed in M. Abon et al., J. Catalysis, Vol. 156, pp. 28-36 (1995).

Approximately 46 g of the 8×14-mesh VO(HPO₄)(H₂O)_(0.5) prepared inComparative Example 3 was heated at 500° C. under a 100 SCCM nitrogenflow for 47 hours to give 37.91 g of light brown particles. XRD analysis(FIG. 5) of this material showed it to be crystalline vanadylpyrophosphate (VO)₂(P₂O₇). The surface properties and bulk compositionof the catalyst prepared in this example are summarized in Table 1. Thevapor phase condensation experiment was carried out according to thedescription in Example 1. The performance of the catalyst is summarizedin Table 4.

This example demonstrates that this catalyst was not as effective atproducing acrylic acid as the invention V—Ti—P catalyst in Example 1 orthe V—Ti—P catalyst in Comparative Example 1. As depicted in the XRDpattern, the surface of this catalyst was composed of crystallinevanadyl pyrophosphate. This discrete species was not observed fromsimilar XRD analysis of the amorphous catalysts described in eitherExample 1 or Comparative Example 1.

Comparative Example 5 Preparation of a Crystalline V—Ti—P—Mo Catalystvia Method F and Reactor Screening with an Aqueous Liquid Feed

The catalyst was prepared according to the procedure described in C. D.Rodica et al., RO 114 084 B1 (1999), except that graphite was not addedto the catalyst.

Vanadium(V) oxide (3.9 g) was mixed with titanium dioxide (6.65 g),molybdenum(VI) oxide (0.45 g), and 85% phosphoric acid (17 mL) in aceramic dish to give a thick paste. This material was then dried at 200°C. in a muffle furnace in air for 3 hours to give a hard yellow solid.The solid was then crushed and sieved through an 8×14 mesh. The meshedparticles were calcined in a muffle furnace in air at 300° C. for 2hours. XRD analysis (FIG. 6) of this material showed it to becrystalline titanium dioxide; vanadium and phosphorus components werenot observed. The surface properties and bulk composition of thecatalyst prepared in this example are summarized in Table 1.

The vapor-phase condensation experiment was carried out as described inComparative Example 1, except that the reaction conditions were set tothose described in RO 114 084 B1. The furnace temperature was set to350° C., liquid feed rate to 0.025 mL/minute, and nitrogen flow to 51SCCM. The feed was composed of a 4:0.67:9 molar mixture of acetic acid,trioxane, and water; the run time was 360 minutes. The performance ofthe catalyst is summarized in Table 4.

This example attempted to reproduce the results disclosed in RO 114 084B1, which claims an acrylic acid yield of 86.3%. However, the actualyield to acrylic acid was found to be less than one percent. Thisresult, combined with the observation that the catalyst containscrystalline TiO₂, provides support for the assertion that titaniumdioxide is an unsuitable precursor for preparing active formaldehydealkanoic acid condensation catalysts.

Example 2 Preparation of an Amorphous V—Ti—P Catalyst via Method G andReactor Screening with an Aqueous Liquid Feed

The catalyst in this example was first prepared by suspending ammoniummetavanadate (19.54 g) in 218.41 g of a 50 wt % titanium(IV)bis(ammonium lactate)dihydroxide solution followed by addition of 200 mLof deionized water in a 1-L three-neck kettle reactor equipped with adistillation head and a mechanical stirrer. The beige suspension wasstirred at 700 rpm for 10 min at room temperature then 105.57 g of 85%phosphoric acid was added followed by a rinse with about 50 mL of water.There was an immediate color change to bright yellow and thickening ofthe mixture, then a change to green then pale green over 20 min. Thesuspension was then heated to reflux (oil bath set at 130° C.) and 220mL of water collected via distillation over three hours. After coolingto room temperature, the resulting pale green semi-solid was scrapedinto a ceramic dish and calcined at 300° C. for 16 h in a muffle furnacein air to give black-green solids, which were sieved through an 8×14mesh. The 8×14 meshed pellets were then calcined at 450° C. in a quartztube furnace for 6 h with a 60 SCCM air flow to give pale green pellets.XRD analysis (FIG. 7) of this material showed it to be primarilyamorphous. The surface properties and bulk composition of the catalystprepared in this example are summarized in Table 1.

The condensation reaction of acetic acid and trioxane (the formaldehydesource) in this example was performed as described in Example 1, exceptthat a liquid feed composed of molar ratio 12 acetic acid/1trioxane/4.09 water was used at 325° C., 0.089 mL liquid feed/minute andthe carrier gas, nitrogen, was set at 70 SCCM. The performance of thecatalyst is summarized in Table 5.

This example demonstrates that (a) using the water-soluble TBALDH allowsfor a more rapid catalyst synthesis in that all three catalystprecursors are combined in a one-pot approach and (b) using TBALDH asthe titanium source for the V—Ti—P material produces an active catalystfor acrylic acid production, even though lactic acid was absent in thecatalyst preparation. The resulting catalyst was amorphous by XRD andhas a surface area very similar to the catalyst described in Example 1and bulk composition very similar to those of the catalysts described inExample 1 and Comparative Example 1.

Comparative Example 6 Preparation of a Crystalline V—Ti—P Catalyst viaMethod H and Reactor Screening with an Anhydrous Liquid Feed

The catalyst in this example was prepared according to the proceduredescribed in Comparative Example 1, except that lactic acid was excludedfrom the procedure. XRD analysis (FIG. 8) of this material showed it tobe a mixture of crystalline vanadium(III) catena-phosphate and titaniumdiphosphate. The surface properties and bulk composition of the catalystprepared in this example are summarized in Table 1. The vapor-phasecondensation reaction was carried out as described in Example 1. Theperformance of the catalyst is summarized in performance Table 5.

This example demonstrates that a V—Ti—P material having low acidity andsurface area is obtained when tetrachlorotitanium was used as thetitanium precursor and lactic acid was excluded during the catalystsynthesis. The surface of the resulting solid was a mixture ofcrystalline compounds, which evidently displayed poor catalytic activitytoward acrylic acid synthesis. The yield was less than 10%, and theselectivity less than 12%. This example also highlights the fact thatTBALDH is a more attractive V—Ti—P precursor, since the lactate groupsinherent in the salt are sufficient to reduce vanadium during catalystsynthesis, which assists in forming an amorphous surface and creatingincreased surface area upon calcination.

Example 3 V—Ti—P Catalyst (Method A at 2× Scale) Lifetime Study with anAnhydrous Liquid Feed

The catalyst in this example was prepared via Method A (Example 1), butat twice the scale. The condensation reaction of acetic acid andtrioxane (the formaldehyde source) in this example was performed asdescribed in Example 1, except that a liquid feed composed of molarratio 12 acetic acid/1 trioxane was used at 325° C., 0.083 mL liquidfeed/minute, and the carrier gases were nitrogen (49 SCCM) and air (21SCCM). The reaction was run for twenty-seven hours. Also, a 25-mm outerdiameter (21 mm inner diameter) quartz reactor tube with length=79 cm(31 inches) was used. Heat to the reactor was provided by an AppliedTest Systems series 3210 three-element electric furnace having a heatedzone 50 cm (19.5 inches) in length. Liquid products were collected in athree-necked flask fitted with a glycol chilled (0° C.) jacket. Thethird neck of the flask was connected to a water-cooled condenser, whichwas connected to a dry ice trap. The base of the receiver flask wasfitted with a stopcock to allow for draining of the liquid products.

The quartz reactor had indentations 13 cm (5 inches) up from the base ofthe tube. The region of the reactor with the indentations was situatednear the base of the heated section of the furnace. The reactor was alsofitted with a thermowell that extended from the top of the reactor toabout an inch below the indentations. The reactor was first loaded withquartz chips to about 8 inches in height above the indentations to allowthe catalyst to be positioned in the middle of the 3-element furnace.The reactor was then loaded with a 5.0 g charge of catalyst. Thethermocouple in the thermowell was placed 1.5 inches up from the base ofthe catalyst bed. Sufficient quartz chips were added to the region abovethe catalyst charge to reach the top of the heated region of the3-element furnace.

Liquid samples were collected over a measured time period, weighed, andanalyzed by gas chromatography and HPLC. Performance of the catalyst issummarized in Table 6.

This example demonstrates that the invention V—Ti—P catalyst preparedwith TBALDH afforded acrylic acid in moderate yield and selectivity overa twenty-seven hour period. The presence of oxygen contributed to anextended catalyst lifetime. As a consequence of using an anhydrousliquid feed, high coking rates are suspected to have caused thedecreased yield observed in the last data point.

Comparative Example 7 V—Ti—P Catalyst (Method B at 2× Scale) LifetimeStudy with an Anhydrous Liquid Feed

The catalyst in this example was prepared via Method B (ComparativeExample 1), but at twice the scale. The vapor-phase condensationexperiment was carried out as described in Example 3. The performance ofthe catalyst is summarized in Table 7.

This example demonstrates that the V—Ti—P catalyst prepared according tothe prior art performed similarly to the invention catalyst when ananhydrous liquid feed was employed over a twenty-seven hour period.Again, the decreased yield observed in the third data point isattributed to a high rate of coking.

Example 4 V—Ti—P Catalyst (Method A at 2× Scale) Lifetime Study with anAqueous Liquid Feed

The catalyst used in this example was the same catalyst charge used inExample 3, except that it was regenerated after that example by heatingat 400° C. under 6 vol % oxygen (94 vol % nitrogen) for 16 hours. Thevapor-phase condensation reaction was then carried out according toExample 3, except that a liquid feed composed of molar ratio 12 aceticacid/1 trioxane/4.09 water was used at 325° C., 0.089 mL liquidfeed/minute. The carrier gases were nitrogen (49 SCCM) and air (21SCCM). The reaction was run for twenty-seven hours. The performance ofthe catalyst is summarized in Table 8.

This example demonstrates that the V—Ti—P catalyst prepared with TBALDHmaintained (1) a very high selectivity toward acrylic acid when anaqueous liquid feed was used and (2) a consistent moderate yield. Thefinal yield of nearly 55% is comparatively higher than the same point inExample 3, presumably due to a lower rate of coking.

Comparative Example 8 V—Ti—P Catalyst (Method B at 2× Scale) LifetimeStudy with an Aqueous Liquid Feed

The catalyst used in this example was the same catalyst charge used inComparative Example 7, except that it was regenerated after that exampleby heating at 400° C. under 6 vol % oxygen (94 vol % nitrogen) for 16hours. The vapor-phase condensation reaction was then carried outaccording to Example 3, except that a liquid feed composed of molarratio 12 acetic acid/1 trioxane/4.09 water was used at 325° C., 0.089 mLliquid feed/minute. The carrier gases were nitrogen (49 SCCM) and air(21 SCCM). The reaction was run for twenty-seven hours. The performanceof the catalyst is summarized in Table 9.

This example demonstrates that the V—Ti—P catalyst prepared according tothe prior art did not afford acrylic acid in as high a yield as theinvention catalyst when an aqueous liquid feed was used. Even though theselectivity toward acrylic acid was similarly high and the reactionlifetime was comparable, the formaldehyde conversion was consistentlylower than observed in Example 4 by more than twenty percent. This issurprising given that both V—Ti—P catalysts demonstrated similaractivity and selectivity when the anhydrous liquid feed was used.

Example 5 Preparation of an Amorphous V—Ti—P Catalyst using Anti-Solventvia Method I and Reactor Screening with an Aqueous Liquid Feed

The catalyst used in this example was prepared by first suspendingammonium metavanadate (19.65 g) in 218.54 g of a 50 wt % titanium(IV)bis(ammonium lactate)dihydroxide solution followed by addition of 150 mLof deionized water in a 1-L three-neck kettle reactor equipped with areflux condenser and a mechanical stirrer. The beige suspension wasstirred at 700 rpm for 10 min at room temperature. Then 105.06 g of 85%phosphoric acid were added slowly followed by a rinse with 50 mL ofdeionized water. There was an immediate color change to bright yellow,then a change to green then pale green over 20 min. The suspension wasthen heated to reflux for one hour, after which no further color changewas observed. The reactor was cooled to about 6° C. in an ice-waterbath, and 700 to 800 mL of absolute ethanol was added, causing themixture to thicken. The contents were stirred for 20 min at 6° C. andthe solids were collected on a medium porosity frit while pulling avacuum. The emerald green filtrate (405.28 g) was collected andsubjected to elemental analysis.

The filtered solid was allowed to air dry while pulling a vacuum on thefrit to give a pale green powder. The powder was calcined initially byheating at 300° C. for 16 h in a muffle furnace in air to givegrey-green solids. The solids were then sieved through an 8×14 mesh. The8×14 meshed pellets were then calcined at 450° C. in a quartz tubefurnace for 6 h with a 60 SCCM air flow to give pale green irregularlyshaped pellets.

The x-ray diffraction pattern (FIG. 9) shows that the catalyst isprimarily amorphous. The surface properties and bulk composition of thecatalyst prepared in this example are summarized in Table 1. The percentvanadium, titanium, and phosphorus lost in the filtrate are summarizedin Table 2. The vapor-phase condensation experiment was performedaccording to Example 4. The performance of the catalyst is summarized inTable 10.

This example demonstrates that the V—Ti—P material obtained byprecipitation from ethanol effectively catalyzed the condensation offormaldehyde with acetic acid to form acrylic acid. Specifically, thecatalyst maintained a formaldehyde conversion of around 78% after 27hours and a product selectivity of approximately 80% after the same timeperiod. Only 7 wt % of the vanadium components and 15.5 wt % of thephosphorus components were lost as a result of filtration.

Example 6 Preparation of an Amorphous V—Ti—P Catalyst withoutAnti-Solvent via Method J and Reactor Screening with an Aqueous LiquidFeed

The catalyst used in this example was prepared by first suspendingammonium metavanadate (19.52 g) in 218.34 g of a 50 wt % titanium(IV)bis(ammonium lactate)dihydroxide solution followed by addition of 150 mLof deionized water in a 1-L three-neck kettle reactor equipped with areflux condenser and a mechanical stirrer. The beige suspension wasstirred at 700 rpm for 10 min at room temperature. Then 105.32 g of 85%phosphoric acid were added slowly followed by a rinse with 50 mL ofdeionized water. There was an immediate color change to bright yellow,then a change to green then pale green over 20 min. The suspension wasthen heated to reflux for one hour, after which no further color changewas observed. The reactor was cooled to about 6° C. in an ice-water bathand 800 mL of deionized water were added. The contents were stirred for20 min at 6° C. and the solids were collected on a medium porosity fritwhile pulling a vacuum. The deep blue filtrate (459.9 g) was collectedand subjected to elemental analysis.

The filtered solid was allowed to air dry while pulling a vacuum on thefrit to give a pale green powder that was calcined initially by heatingat 300° C. for 16 h in a muffle furnace in air to give grey-greensolids. The solids were then sieved through an 8×14 mesh. The 8×14meshed pellets were then calcined at 450° C. in a quartz tube furnacefor 6 h with a 60 SCCM air flow to give yellow irregularly shapedpellets.

The x-ray diffraction pattern (FIG. 10) shows that the catalyst wasprimarily amorphous. The surface properties and bulk composition of thecatalyst prepared in this example are summarized in Table 1. The percentvanadium, titanium, and phosphorus lost in the filtrate are summarizedin Table 2. The vapor-phase condensation experiment was carried out asdescribed in Example 4. The performance of the catalyst is summarized inTable 11.

This example demonstrates that isolating the V—Ti—P catalyst byfiltration in the absence of an anti-solvent such as ethanol led to amaterial with a relatively high titanium content and a loss of nearly 36wt % of both the vanadium and phosphorus components. Moreover, theresulting material did not carry out the condensation reaction aseffectively as the V—Ti—P material in Example 5. For example, althoughthe formaldehyde conversion was initially high (>90%), the selectivityto acrylic acid was comparatively low (approximately 59% after a 27-hourperiod). Moreover, the yield of this reaction at 27 hours was abouttwenty percent lower than that of Example 5.

A summary of the XRD measurements for the catalysts produced is givenbelow.

Semi-Crystalline Catalysts:

Calculated Estimated Weight % of Crystallite Phase from Size Example No.Crystalline Phase Identified Rietveld Method of Phase (Å) Comp. Ex. 2(Fig. 3) Rutile Titanium dioxide (TiO₂) 21 191 Comp. Ex. 3 (Fig. 4)Vanadyl Hydrogenphosphate Hemihydrate 96 723 Comp. Ex. 4 (Fig. 5)Bis(oxovandium) Diphosphate 94 198 Comp. Ex. 5 (Fig. 6) Titanium Dioxide97 116 Comp. Ex. 6 (Fig. 8) Vanadium (III) Catena V(PO₃)₃ 34 670Titanium Diphosphate (V)-Ti(P₂O₇) 66 424

Amorphous Catalysts:

2-Theta Peak Estimated Crystallite Example No. Locations Relative AreaSize (Å) Ex. 1 (FIG. 1) 26.0 59.3 100 58 <30 <30 Ex. 2 (FIG. 7) 25.660.2 100 61 <30 <30 Ex. 5 (FIG. 9) 25.3 61.4 100 82 <30 <30 Comp. Ex. 1(FIG. 2) 25.6 59.2 100 57 <30 <30 Ex. 6 (FIG. 10) 25.7 60.2 100 86 <30<30

TABLE 1 BET Iso-Propanol Surface TPD Catalyst Area Total Acid Mole RatioBulk Example Descriptor (m²/g) Sites (μmol/g) XRD Composition (via XRF)Ex. 1 V-Ti-P 55 92.5 Amorphous 1.00V:1.92Ti:5.34P (Method A) Comp. Ex. 1V-Ti-P 34 64.2 Amorphous 1.00V:1.89Ti:5.29P (Method B) Comp. Ex. 2V-Ti-P 1.7 2.8 Rutile 1.00V:1.07Ti:3.03P (Method C) Comp. Ex. 3 V-P 76.8 VO(HPO₄)(H₂O)_(0.5) 1.00V:0.96P (Method D) Comp. Ex. 4 V-P 21 17.6(VO)₂(P₂O₇) 1.00V:1.00P (Method E) Comp. Ex. 5 V-Ti-P-Mo 73 89.4 TiO₂n/a (Method F) Ex. 2 V-Ti-P 55 n/a Amorphous 1.00V:2.00Ti:5.33P (MethodG) Comp. Ex. 6 V-Ti-P 5.3 13.6 V(PO₃)₃ and 1.00V:1.78Ti:5.22P (Method H)Ti(P₂O₇) Ex. 5 V-Ti-P 46 84.5 Amorphous 1.00V:1.94Ti:4.92P (Method I)Ex. 6 V-Ti-P 78 143.4 Amorphous 1.00V:2.61Ti:4.58P (Method J)

TABLE 2 Example 5 Example 6 V-Ti-P V-Ti-P Catalyst Descriptor (Method I)(Method J) Vanadium in precursor (g) 8.56 8.5 Titanium in precursor (g)17.78 17.77 Phosphorus in precursor (g) 28.23 28.3 Vanadium in filtrate(g), 0.6 3.054 measured via XRF Titanium in filtrate (g), 0.002 0.056measured via XRF Phosphorus in filtrate (g), 4.377 10.256 measured viaXRF Wt Percent vanadium 7.0 35.9 lost in catalyst synthesis Wt Percenttitanium lost in 0.0 0.3 catalyst synthesis Wt Percent phosphorus 15.536.2 lost in catalyst synthesis

TABLE 3 Comp. Comp. Example 1 Example 1 Example 2 V-Ti-P V-Ti-P V-Ti-PCatalyst Descriptor (Method A) (Method B) (Method C) Furnace temperature(° C.) 325 325 325 Reaction time (min.) 180 180 180 Nitrogen flow rate(SCCM) 80 80 80 Liquid feed molar ratio 12/1 12/1 12/1 (HOAc/Trioxane)Liquid feed rate 0.083 0.083 0.083 Product, g 14.4 14.083 13.53Reactants fed, g 15.84 15.84 15.84 GC Results Acetone, wt % 0.16 0 0MeOAc, wt % 0.11 0 0 Water, wt % 6.96 5.99 0.52 HOAc, wt % 70.71 70.1487.1 Acrylic acid, wt % 18.75 20.07 0 HOPr 0 0.06 0 Total knowns, wt %96.73 96.26 87.62 Key Metrics % yield acrylic acid from 64.35 68.06 0.00H2CO total mole acrylates/kg-hr 2.5 2.66 0.00 mole ratio AA/acetone94.45 182.78 0.00 % HOAc accountability 88.68 88.01 83.72

TABLE 4 Comp. Comp. Comp. Example 3 Example 4 Example 5 V-P V-PV-Ti-P-Mo Catalyst Descriptor (Method D) (Method E) (Method F) Furnacetemperature (° C.) 325 325 350 Reaction time (min.) 180 180 360 Nitrogenflow rate (SCCM) 80 80 51 Liquid feed molar ratio 12/1/0 12/1/0 4/0.67/9(HOAc/Trioxane/H2O) Liquid feed rate 0.083 0.083 0.025 Product, g 13.6214.29 8.61 Reactants fed, g 15.84 15.84 9.7 GC Results Acetone, wt %0.06 MeOAc, wt % 0.11 Water, wt % 2.67 4.13 33.87 HOAc, wt % 73.91 75.7952.08 Acrylic acid, wt % 4.89 13.32 0.49 HOPr Total knowns, wt % 87.8399.19 86.55 Key Metrics % yield acrylic acid from 15.87 45.37 1.4 H2COtotal mole acrylates/kg-hr 0.62 1.76 0.02 mole ratio AA/acetone % HOAcaccountability 75.39 88.26 63.4

TABLE 5 Comparative Example 2 Example 6 V-Ti-P V-Ti-P CatalystDescriptor (Method G) (Method H) Nitrogen flow rate (SCCM) 70 80 Liquidfeed molar ratio 12/1/4.09 12/1/0 (HOAc/Trioxane/H2O) Liquid feed rate0.089 0.083 Product, g 14.45 10.08 Reactants fed, g 16.19 15.84 GC/HPLCResults Formaldehyde, wt % 2.68 5.71 Acetone, wt % 0.013 0.29 MeOAc, wt% 0.031 Water, wt % 13.06 1.28 HOAc, wt % 72.21 89.33 Acrylic acid, wt %17.33 3.18 HOPr, wt % Total knowns, wt % 105.32 99.79 Key Metrics % H2COconversion 77.84 67.08 % selectivity to acrylic acid 76.74 11.39 fromH2CO % yield acrylic acid from 59.73 7.64 H2CO % HOAc accountability89.69 66.24 mole acrylic acid/kg-hr 2.32 0.3

TABLE 6 Example 3 Catalyst Descriptor V-Ti-P, Method A (2X Scale) Liquidfeed molar ratio 12/1 (HOAc/Trioxane) Liquid feed flow rate 0.083(mL/min) Nitrogen flow rate (SCCM) 49 Air flow rate (SCCM) 21 Timebetween samples (h) 1.0 3.0 23 Total run time (h) 1.0 4.0 27 Product, g4.37 15.19 116.2 Reactants fed, g 5.24 15.84 121.41 GC/HPLC ResultsFormaldehyde, wt % 2.33 3.21 5.31 Acetone, wt % 0.195 0.23 0.227 MeOAc,wt % 0.084 0.073 0.092 Water, wt % 7.57 6.53 4.58 HOAc, wt % 68.34 69.9876.33 Acrylic acid, wt % 17.53 15.97 10.27 HOPr, wt % 0.035 0.047 Totalknowns, wt % 96.05 96.03 96.85 Key Metrics % H2CO conversion 82.54 72.3154.28 % selectivity to acrylic 66.35 79.38 67.88 acid from H2CO % yieldacrylic acid 54.76 57.40 36.85 from H2CO % HOAc accountability 78.1990.42 91.99 mole acrylic acid/kg-hr 2.14 2.24 1.44

TABLE 7 Comparative Example 7 Catalyst Descriptor V-Ti-P, Method B (2XScale) Liquid feed molar ratio 12/1 (HOAc/Trioxane) Liquid feed flowrate (mL/min) 0.083 Nitrogen flow rate (SCCM) 49 Air flow rate (SCCM) 21Time between samples (h) 1.0 3.0 23 Total run time (h) 1.0 4.0 27Product, g 4.85 15.48 119.01 Reactants fed, g 5.39 15.77 121.46 GC/HPLCResults Formaldehyde, wt % 3.94 3.28 5.64 Acetone, wt % 0.08 0.18 0.24MeOAc, wt % 0.08 Water, wt % 8.7 5.49 3.28 HOAc, wt % 68.67 71.21 78.05Acrylic acid, wt % 15.36 17.86 11.07 HOPr, wt % Total knowns, wt % 96.8398.02 98.28 Key Metrics % H2CO conversion 68.12 71.04 50.29 %selectivity to acrylic 76.05 92.50 80.87 acid from H2CO % yield acrylicacid from 51.80 65.71 40.66 H2CO % HOAc accountability 82.68 95.47 96.75mole acrylic acid/kg-hr 2.02 2.57 1.59

TABLE 8 Example 4 Catalyst Descriptor V-Ti-P, Method A (2X Scale) Liquidfeed molar ratio 12/1/4.09 (HOAc/Trioxane/H2O) Liquid feed rate (mL/min)0.089 Nitrogen flow rate (SCCM) 49 Air flow rate (SCCM) 21 Time betweensamples (h) 1.0 3.0 23.1 Total run time (h) 1.0 4.0 27.1 Product, g 5.3416.70 130.42 Reactants fed, g 5.835 17.079 131.680 GC/HPLC ResultsFormaldehyde, wt % 4.18 4.47 4.72 Acetone, wt % 0.073 0.096 0.096 MeOAc,wt % 0.184 0.195 0.206 Water, wt % 17.15 13.44 12.56 HOAc, wt % 66.1470.01 69.44 Acrylic acid, wt % 12.84 13.68 13.57 HOPr, wt % 0.016 0.0050.005 Total knowns, wt % 100.58 101.90 100.60 Key Metrics % H2COconversion 62.49 57.14 54.15 % selectivity to acrylic 76.85 95.67 101.43acid from H2CO % yield acrylic acid from H2CO 48.02 54.67 54.93 % HOAcaccountability 86.62 98.10 98.58 mole acrylic acid/kg-hr 1.86 2.12 2.13

TABLE 9 Comparative Example 8 Catalyst Descriptor V-Ti-P, Method B (2XScale) Liquid feed molar ratio 12/1/4.09 (HOAc/Trioxane/H2O) Liquid feedflow rate (mL/min) 0.089 Nitrogen flow rate (SCCM) 49 Air flow rate(SCCM) 21 Time between samples (h) 1.0 3.0 23 Total reaction time (h)1.0 4.0 27 Product, g 5.42 16.72 130.91 Reactants fed, g 5.762 17.1131.39 GC/HPLC Results Formaldehyde, wt % 6.61 6.87 6.78 Acetone, wt %0.068 0.063 0.065 MeOAc, wt % Water, wt % 8.83 8.96 9.15 HOAc, wt %72.59 73.16 72.15 Acrylic acid, wt % 8.68 8.35 8.98 HOPr, wt % Totalknowns, wt % 96.85 97.4 97.12 Key Metrics % H2CO conversion 39.03 34.1333.75 % selectivity to acrylic acid 85.49 97.78 108.32 from H2CO % yieldacrylic acid from H2CO 33.37 33.37 36.56 % HOAc accountability 92.3696.28 97.52 mole acrylic acid/kg-hr 1.29 1.29 1.42

TABLE 10 Example 5 Catalyst Descriptor V-Ti-P, Method I Liquid feedmolar ratio 12/1/4.09 (HOAc/Trioxane/H2O) Liquid feed rate (mL/min)0.089 Nitrogen flow rate (SCCM) 49 Air flow rate (SCCM) 21 Time betweensamples (h) 1.0 3.0 23.1 Total run time (h) 1.0 4.0 27.1 Product, g 4.8516.06 128.97 Reactants fed, g 5.71 17.14 132.12 GC/HPLC ResultsFormaldehyde, wt % 1.88 2.12 2.31 Acetone, wt % 0.076 0.068 0.062 MeOAc,wt % 0.131 0.102 0.092 Water, wt % 16.51 15.72 15.52 HOAc, wt % 67.3865.84 66.89 Acrylic acid, wt % 16.76 16.84 15.57 HOPr, wt % 0.012 0.012Total knowns, wt % 102.74 100.70 100.46 Key Metrics % H2CO conversion84.35 80.52 77.89 % selectivity to acrylic acid 68.93 80.09 79.75 fromH2CO % yield acrylic acid from 58.15 64.49 62.12 H2CO % HOAcaccountability 85.01 92.09 95.91 mole acrylic acid/kg-hr 2.26 2.50 2.41

TABLE 11 Example 6 Catalyst Descriptor V-Ti-P, Method J Liquid feedmolar ratio 12/1/4.09 (HOAc/Trioxane/H2O) Liquid feed rate (mL/min)0.089 Nitrogen flow rate (SCCM) 49 Air flow rate (SCCM) 21 Time betweensamples (h) 1.0 3.0 23.0 Total run time (h) 1.0 4.0 27.0 Product, g 4.7516.21 126.52 Reactants fed, g 5.69 17.12 131.40 GC/HPLC ResultsFormaldehyde, wt % 0.889 0.917 3.27 Acetone, wt % 0.023 0.024 0.035MeOAc, wt % 0.143 0.154 0.184 Water, wt % 19.89 16.97 15.27 HOAc, wt %65.42 68.77 72.24 Acrylic acid, wt % 14.86 13.69 10.34 HOPr, wt % 0.0260.064 0.065 Total knowns, wt % 101.25 100.58 101.40 Key Metrics % H2COconversion 92.72 91.48 69.12 % selectivity to acrylic 54.71 57.92 58.86acid from H2CO % yield acrylic acid from H2CO 50.72 52.99 40.68 % HOAcaccountability 79.90 93.38 95.79 mole acrylic acid/kg-hr 1.97 2.06 1.58

Condensation Reaction for Examples 7-9

The catalyst used in these examples was a 5.0 g charge obtained from theinvention catalyst batch described in Example 3. The vapor phasecondensation reactions were carried out as described in Example 3. Thespace velocities were varied in Examples 7 and 8, but the molar ratiosof the feed components remained constant. Counting trioxane as threeformaldehyde equivalents and inerts as being nitrogen plus aircomponents other than oxygen, the molar ratios of the feed componentsacetic acid/formaldehyde/water/inerts/oxygen were1.31/0.33/0.45/2.93/0.19.

Samples were taken after 16.02 mL (17.3 g) of the liquid had been fed inorder to minimize any effects due to possible reactant induced catalystdeactivation. Then the samples were weighed and analyzed. The lastsample was taken 1 hour after the liquid feed was stopped. Generally,three samples were taken at each set of conditions, and the results arepresented as an average of the results from the samples collected ateach set of conditions. The results are summarized in Table 12 below.After the reaction at a given set of conditions was completed, thecatalyst was regenerated by subjecting to 10 SCCM nitrogen plus 20.8SCCM air at 405° C. overnight.

Example 7

This example illustrates the invention performed in the lower spacevelocity region of the preferred range. The 1.31/0.33/0.45/2.93/0.19molar ratio of acetic acid/formaldehyde/water/inerts/oxygen mixture wasdelivered to the reactor under the conditions described above at a spacevelocity of 60 moles of all feed components/kg-hr. The reaction evolvedheat, and the catalyst bed temperature during this run was 339.5° C. Theresults are summarized in Table 12 below.

Example 8

This example illustrates the invention performed in the most preferredspace velocity region. The 1.31/0.33/0.45/2.93/0.19 molar ratio ofacetic acid/formaldehyde/water/inerts/oxygen mixture was delivered tothe reactor under the conditions described above at a space velocity of138 moles of all feed components/kg-hr. The reaction evolved heat, andthe catalyst bed temperature during this run was 352.9° C. The resultsare summarized in Table 12 below.

Example 9

This example was performed at a low space velocity value outside of thepreferred range of the invention. The 1.31/0.33/0.45/2.93/0.19 molarratio of acetic acid/formaldehyde/water/inerts/oxygen mixture wasdelivered to the reactor under the conditions described above at a spacevelocity of 26 moles of all feed components/kg-hr. The reaction evolvedheat, and the catalyst bed temperature during this run was 334.2° C. Theresults are summarized in the Table 12 below.

TABLE 12 Ex. 7 Ex. 8 Ex. 9 Space velocity (total moles feed/( kgcatalyst · hr) 60 138 26 % acetic acid accountability 87.2 92.9 80.4Total moles acrylates/kg-hr 2.7 6.1 1.0 % H₂CO conversion 85.0 80.1 91.4% yield acrylates from H₂CO fed 68.5 68.8 60.8 % selectivity toacrylates from H₂CO reacted 80.6 86.0 66.5

Thus, the high space velocity conditions of the invention produced lessacetic acid destruction, higher space time yields, higher yields ofacrylates from formaldehyde equivalents fed and a higher selectivity toacrylates from the formaldehyde reacted. These improvements inperformance more than offset the small decrease in formaldehydeconversion, since the difference in formaldehyde conversion is dueprimarily to less formaldehyde being destroyed by the process of theinvention. Also, formaldehyde would be recycled in a commercial process.

Example 10

This example illustrates that the preferred conditions of the inventionallow for high selectivity and activity to be maintained over anextended period of time without the need for catalyst regeneration. Thereactor set up for this example was similar to that of Examples 7-9,except for two differences. A different furnace was used, and the wallsof this furnace were about 1.5 inches (3.8 cm) from the reactor. Thisconfiguration resulted in lower catalyst bed temperatures than in theprevious examples. The furnace was set at 320° C., and the catalyst bedtemperatures during the reaction ranged between about 327 and 332° C.The second difference is that the receiver was kept at ambienttemperature instead of 0° C. The 1.31/0.33/0.45/2.93/0.19 molar ratio ofacetic acid/formaldehyde/water/inerts/oxygen mixture was delivered tothe reactor at a space velocity of 138 moles of all feedcomponents/kg-hr. The reaction was run continuously without interruptionor any catalyst regeneration. Two samples were collected during thefirst day of operation. Then one sample was collected per day. Table 13below summarizes the performance of the preferred process of theinvention on day 4, 17, and 31 of continuous operation without anyregeneration.

TABLE 13 Day 4 17 31 % acetic acid accountability 98.7 99.7 98.9 Totalmoles acrylates/kg-hr 4.7 4.4 4.4 % H₂CO conversion 55.0 50.6 54.5 %yield acrylates from H₂CO fed 52.5 49.6 49.3 % selectivity to acrylatesfrom H₂CO reacted 95.4 97.9 90.4

Examples 11 through 25 below exemplify the preparation of the supportedcatalysts of the invention. Examples 26 through 37 demonstrate theutility of the supported catalysts of the invention in the preparationof acrylic acid from acetic acid and a formaldehyde source.

Example 11

A solution was prepared from ammonium vanadate (0.97 g, 8.29 mmole),water (10 mL), and oxalic acid (2.09 g, 16.58 mmole). The ammoniumvanadate dissolved without heating with the evolution of gas to form ablue solution. The soluble Ti source used in this example wastitanium(IV) bis(ammonium lactate)dihydroxide, 50 wt % in water(TBALDH), certified to contain 13.4 wt % TiO₂. 9.886 g (0.0166 mole Ti)of the TBALDH solution were added to the aqueous V/oxalic acid solution.The solution remained clear blue with no precipitate. Since gas wasevolved from the solution, an accurate weight was needed for thissolution to be used for impregnations. By weighing theflask+stirrer+solution and subtracting the weight of the dry flask andstirrer, the weight of the solution was 22.42 g (22.28 g was transferredto a storage bottle). Each gram of this solution contained 0.3698 mmoleV (18.83 mg) and 0.7395 mmole Ti (35.42 mg). The density of thissolution was 1.15 g/mL.

Example 12

A test was performed to test how the solution of Example 11 behaved whendried and how the dried mass reacted with aqueous H₃PO₄. 1.560 g of thesolution of Example 11 was placed in an evaporating dish and heated onthe steam bath. This produced a dark blue-green glass (0.440 g). Thisglass was treated with a solution prepared from 0.401 g 85% H₃PO₄(calculated amount 0.379 g) diluted to 1.3 mL with water. At first,about 20% of the glass dissolved to form a clear green solution, butthen the whole system set up as a thick light-green paste.

Example 13

A TiO₂ supported catalyst precursor was prepared using a portion of thesolution from Example 11 (4.08 g) and TiO₂ 1/16-inch extrudates (5.0 g,Alfa Aesar lot # K21S005). These conditions were about incipientwetness. The white TiO₂ turned gray upon impregnation. The impregnatedTiO₂ was dried on the steam bath with occasional stirring. The steambath-dried material was light gray. This material was dried in themuffle furnace overnight at 110° C. The material was light gray-tan uponremoval from the muffle furnace. Phosphorus was added to the catalystprecursor using an aqueous solution of phosphoric acid by incipientwetness with the solution prepared to contain sufficient phosphorus togive a P/V molar ratio=5.5. The amount of solution required wascalculated from the measured density of solution of Example 11 (1.15g/mL) that was used to prepare the original catalyst precursor such thatthe volume of the aqueous phosphoric acid solution was the same as thatof the solution of Example 11 originally used. A solution was preparedfrom 0.996 g 85% H₃PO₄ (calculated amount 0.992 g) diluted to 3.5 mLwith water and used to impregnate the material recovered from the mufflefurnace. The resulting impregnated material was very light green. Thephosphoric acid impregnated sample appeared to be at incipient wetnessand was stirred with a Teflon spatula in its evaporating dish on thesteam bath until free flowing. The color remained green, but became alighter shade as the water evaporated. The sample in its evaporatingdish was placed in the muffle furnace and heated to 110° C. for 2 hoursthen heated to 450° C. for 6 hours. The resulting catalyst (5.912 g) wasyellow.

Example 14

A SiO₂ supported catalyst precursor was prepared using a portion of thesolution from Example 11 (6.82 g) and 8 mesh Davison grade 57 SiO₂ (5.0g, lot 557). These conditions were about incipient wetness. The wetimpregnated SiO₂ was dark blue. This material was dried on the steambath with occasional stirring. The steam bath-dried material was lightblue. This material was dried in the muffle furnace over night at 110°C. The material was dark blue upon removal from the muffle furnace.

Phosphorus was added to the catalyst precursor using an aqueous solutionof phosphoric acid by incipient wetness with the solution prepared tocontain sufficient phosphorous to give a PN molar ratio=5.5. The amountof solution required was calculated from the measured density ofsolution of Example 11 (1.15 g/mL) that was used to prepare the originalcatalyst precursor such that the volume of the aqueous phosphoric acidsolution was the same as that of the solution of Example 11 originallyused. A solution was prepared from 1.654 g 85% H₃PO₄ (calculated amount1.658 g) diluted to 5.9 mL with water and used to impregnate thematerial recovered from the muffle furnace. The resulting impregnatedmaterial was very dark green.

The phosphoric acid impregnated sample appeared to be at incipientwetness and was stirred with a Teflon spatula in its evaporating dish onthe steam bath until free flowing. The color remained green, but becamea lighter shade as the water evaporated. The sample in its evaporatingdish was placed in the muffle furnace and heated to 110° C. for 2 hours,then heated to 450° C. for 6 hours. The resulting catalyst (6.572 g) wasgreen with orange regions and looked most like the bulk V/2Ti/5.5P oxidecatalyst.

Example 15

An alumina supported catalyst precursor was prepared using a portion ofthe solution from Example 11 (7.24 g) and high surface area aluminumoxide ⅛-inch extrudates (5.0 g, Alfa Aesar lot no A22M20, stock no43832, bimodal pore distribution, surface area approximately 255 m2/g).During the preparation, too much solution (9.094 g) was added, and aportion (discarded) was removed with a dropper to bring the amount ofthe solution remaining to 7.24 g. With this amount of solution, thecatalyst was wet, but little solution was visible on the evaporatingdish. The catalyst precursor was blue when initially impregnated. It wasdried on the steam bath with occasional stirring. The steam bath-driedmaterial was light gray. This material was dried in the muffle furnaceover night at 110° C. The material was light gray-tan upon removal fromthe muffle furnace.

Phosphorus was added to the catalyst precursor using an aqueous solutionof phosphoric acid by incipient wetness with the solution prepared tocontain sufficient phosphorous to give a PN molar ratio=5.5. The amountof solution required was calculated from the measured density ofsolution of Example 11 (1.15 g/mL) that was used to prepare the originalcatalyst precursor such that the volume of the aqueous phosphoric acidsolution was the same as that of the solution of Example 11 originallyused. A solution was prepared from 1.761 g 85% H₃PO₄ (calculated amount1.760 g) diluted to 6.3 mL with water and used to impregnate thematerial recovered from the muffle furnace. The resulting impregnatedmaterial was light green.

The phosphoric acid impregnated sample appeared to be at incipientwetness and was stirred with a Teflon spatula in its evaporating dish onthe steam bath until free flowing. The color remained green, but becamea lighter shade as the water evaporated. The sample in its evaporatingdish was placed in the muffle furnace and heated to 110° C. for 2 hours,then heated to 450° C. for 6 hours. The resulting catalyst (6.802 g) waslight green and the extrudates had some cracks in them.

Example 16

An aqueous V/Ti solution was prepared as follows. Ammonium vanadate(0.97 g, 8.28 mmole) and oxalic acid dehydrate (2.09 g, 16.58 mmole)were dissolved in water with stirring at room temperature. The color ofthis solution changed over the course of an hour from orange to red tobrown to brown/green (with the evolution of bubbles) to dark green todark blue. After waiting about an additional hour, no gas evolution wasseen from the blue solution. About 240 mg gas had evolved based on theweight loss of the solution. TBALDH solution (9.89 g, 16.6 mmole Ti) wasadded to yield a dark blue solution (22.62 g). Each gram of thissolution contained 0.3665 mmole V (18.67 mg) and 0.7339 mmole Ti (35.15mg).

A zirconium oxide supported catalyst was prepared from a portion of thissolution (2.355 g) and zirconium oxide catalyst support (5.0 g, AlfaAesar lot # B21T010) ⅛-inch extrudates. This amount was close toincipient wetness and the wet catalyst in the evaporating dish had alight blue color. The impregnated material was dried with stirring onthe steam bath to yield a material with very light blue color. Thismaterial was placed in the muffle furnace and dried overnight at 110° C.The material recovered from the muffle furnace was light gray-tancolored.

In theory, this catalyst contained 0.8631 eq V, so 5.5 times that amount(4.747 mmole) of phosphorus was required for the second impregnation or547.3 mg 85% H₃PO₄. A solution was prepared from 547 mg 85% H₃PO₄ anddiluted with water to a volume=2.0 mL. The sample of the materialrecovered from the muffle furnace was placed in a clean evaporating dishand impregnated with the aqueous H₃PO₄ solution. The conditions used inthis impregnation were close to incipient wetness (some liquid alsowetted the evaporating dish). The mixture was dried with stirring with aTeflon spatula until free flowing. The steam bath dried material waslight green and looked homogeneous. It was placed in the muffle furnaceand dried at 110° C. for 2 hours.

The material recovered from the muffle furnace was gray-tan colored. Itwas kept in the same evaporating dish and calcined in the muffle furnacefor 6 hours at 450° C. The material recovered from the muffle furnace(5.45 g) was uniformly yellow.

Example 17

The catalyst of this example was designed to have the approximate ratiosof added species: V/Ti/P=1/2/5.5 (neglecting the TiO₂ support). Thecatalyst precursor was 2.4 wt % V on TiO₂ extrudates prepared fromaqueous VCl₃ and 1/16-inch TiO₂ extrudates followed by calcinations at500° C. for 2 hours. 5.0 grams of this catalyst were placed in anevaporating dish and impregnated with 2.81 g titanium(IV) bis(ammoniumlactate)dihydroxide, 50 wt % in water (TBALDH), certified to contain13.4 wt % TiO₂, while stirring. This amount of the TBALDH solution (ca.2.3 mL) was about right for incipient wetness impregnation, and thecatalyst surface was wet, but there was no puddle in the evaporatingdish. The starting charge of the V/TiO₂ catalyst contained approximately2.356 mmole V, and the TBALDH solution contained about twice this amountof Ti (about 4.71 mmole). The evaporating dish containing theTi-impregnated V/TiO₂ material was placed into a muffle furnace andheated at 110° C. overnight. The catalyst recovered from the mufflefurnace has a gray color whereas the starting V/TiO₂ catalyst was lighttan. This material was impregnated with a mixture prepared from 85%H₃PO₄ (1.494 g, 12.96 mmole P) diluted to 2.3 mL with water. This amountof solution was also very close to incipient wetness, although the baseof the evaporating dish was also wet. The evaporating dish was placed onthe steam bath and heated with occasional stirring until the extrudatesappeared dry. The evaporating dish was placed in the muffle furnace anddried at 110° C. for two hours, then at 500° C. for 6 hours. Thematerial recovered from the muffle furnace (6.16) g was a darker tanthan the starting V/TiO₂ material (sort of a gray-tan).

Example 18

This example illustrates the use a more concentrated V/Ti aqueoussolution where the ammonium vanadate and oxalic acid were not dissolvedin water first (unlike the case of Example 11). This allows for a singleincipient wetness impregnation of these two metals to provide abouttwice the loading on the silica support as in Example 14. A solution wasprepared from ammonium vanadate (0.97 g, 8.29 mmole), titanium(IV)bis(ammonium lactate)dihydroxide (50 wt % in water (TBALDH) certified tocontain 13.4 wt % TiO₂) (9.886 g, 16.6 mmole Ti, of the TBALDHsolution), and oxalic acid dehydrate (2.09 g, 16.58 mmole). After anhour, a dark blue solution resulted with mass=12.89 g. 1 gram of thissolution contained 0.643 mmole V (32.76 mg) and 1.288 mmole Ti (61.69mg).

Davison 8 mesh grade 57 SiO₂ (5.0 g, Lot 557) was loaded into anevaporating dish. This SiO₂ was loaded with the V/Ti aqueous solution(7.959 g) to the point of incipient wetness (7.63 g were required forabout a 5 wt. % V loading). This material was stirred on the steam bathuntil dry and free flowing. It was then transferred to the mufflefurnace and heated to 110° C. for 4 hours. The material recovered fromthe muffle furnace (8.454 g) was light blue and was fairly uniformlyimpregnated (note the material Example 14 was dark blue at this stage ofthe process).

A solution was prepared from 85% phosphoric acid (3.245 g, 28.147 mmole)and diluted to 5.9 mL with water. This amount of P is a 5.5 molar excessover the amount of V already on the silica. The silica containing the Vand Ti in the evaporating dish was impregnated with all of the aqueousphosphoric acid solution. The 5.9 mL charge was slightly in excess ofthe amount required for incipient wetness (perhaps by about 0.5 mL). Thecatalyst immediately became dark green, and the residual liquid portionwas green. The mixture was heated on the steam bath with stirring untilthe material was free flowing and there was no sign of any precipitationin the green liquid as it was evaporated (suggesting some degree ofsolubility of the V in the aqueous phosphoric acid solution). Steam bathdried material was light green and appeared to be fairly uniformlyimpregnated. It was placed in the muffle furnace and heated overnight at110° C. The material obtained from the 110° C. muffle furnace (10.381 g)was light green. 10.326 g of this material were transferred to a newevaporating dish. This material was placed in the muffle furnace andheated at 450° C. for 6 hours. 8.194 grams of green catalyst wererecovered from the muffle furnace.

Example 19

A solution was prepared from ammonium vanadate (4.85 g, 41.5 mmole),oxalic acid (10.45 g, 82.9 mmole), and water (50 mL). The initial massof this solution was 64.91 g, and the mass after the gas evolution hadceased was 63.31 g (loss of 1.60 g). The aqueous TBALDH solution (49.43g, 83.0 mmole Ti) was added to the ammonium vanadate solution. The massof the resulting solution was 112.76 g. Each gram of this solution wascalculated to contain 0.368 mmole V (18.74 mg) and 0.736 mmole Ti (35.26mg).

Silica chunks (50.02 g, 8 mesh, Davison Grade 57, Lot 557) were placedin an evaporating dish. The silica in the evaporating dish wasimpregnated to incipient wetness with a portion of the solution (76.43g). The mixture was dried with occasional stirring on the steam bathuntil free flowing and light blue, then dried further in the mufflefurnace at 110° C. overnight. 64.31 grams were recovered from the mufflefurnace. The catalyst contained 28.13 mmole V. Each gram contained0.4374 mmole V (22.28 mg). The catalyst was divided up into 6 gramportions for phosphorus loading, so a 6 g charge contained 2.2244 mmoleV.

One feature of the invention is that once the V and Ti are on thesupport, many different catalysts can be prepared by using differentamounts of the phosphorus component to be loaded onto the catalyst asillustrated in Examples 20 through 23.

Example 20

This example illustrates the preparation of a molar ratio V/2Ti/3.5Poxide catalyst. 6.0 g of the Example 19 catalyst were placed in anevaporating dish. This catalyst was impregnated with a solution preparedfrom 85% H₃PO₄ (1.06 g, 9.18 mmole P) diluted to 5.5 mL (the 5.5 mLdilution provided incipient wetness with this amount of catalystprecursor). The mixture was stirred on the steam bath until freeflowing. The catalyst precursor sample was placed in the muffle furnaceand dried at 110° C. for one hour. The dried catalyst was transferred toa clean evaporating dish, returned to the muffle furnace, and thencalcined at 450° C. for 6 hours. 5.789 g were recovered.

Example 21

This example illustrates the preparation of a molar ratio V/2Ti/4.0Poxide catalyst. 6.0 g of the Example 19 catalyst were placed in anevaporating dish. This catalyst was impregnated with a solution preparedfrom 85% H₃PO₄ (1.21 g, 10.50 mmole P) diluted to 5.5 mL. The mixturewas stirred on the steam bath until free flowing. The catalyst precursorsample was placed in the muffle furnace and dried at 110° C. for onehour. The dried catalyst was transferred to a clean evaporating dish,returned to the muffle furnace, and then calcined at 450° C. for 6hours. 5.855 g were recovered.

Example 22

This example illustrates the preparation of a molar ratio V/2Ti/4.5Poxide catalyst. 6.0 g of the Example 19 catalyst were placed in anevaporating dish. This catalyst was impregnated with a solution preparedfrom 85% H₃PO₄ (1.36 g, 11.81 mmole P) diluted to 5.5 mL. The mixturewas stirred on the steam bath until free flowing. The catalyst precursorsample was placed in the muffle furnace and dried at 110° C. for onehour. The dried catalyst was transferred to a clean evaporating dish,returned to the muffle furnace, and then calcined at 450° C. for 6hours. 5.999 g were recovered.

Example 23

This example illustrates the preparation of a molar ratio V/2Ti/5.0Poxide catalyst. 6.0 g of the Example 19 catalyst were placed in anevaporating dish. This catalyst was impregnated with a solution preparedfrom 85% H₃PO₄ (1.51 g, 13.12 mmole P) diluted to 5.5 mL. The mixturewas stirred on the steam bath until free flowing. The catalyst precursorsample was placed in the muffle furnace and dried at 110° C. for onehour. The dried catalyst was transferred to a clean evaporating dish,returned to the muffle furnace, and then calcined at 450° C. for 6hours. 6.085 g were recovered.

Example 24

A supported catalyst comprising 5 mole % vanadium and 10 mole %phosphorus was prepared in the following way: A white crystallinetitanium pyrophosphate (TiP₂O₇) with a specific surface area of 100 m²/gwas first prepared according to the procedure described in I. C. Marcuet al., J. Mol. Catal., Vol. 203, pp. 241-250 (2003), then crushed andsieved through an 8×14 mesh. A solution was prepared from ammoniumvanadate (0.164 g, 0.0014 mole), 85% H₃PO₄ (0.326 g, 2.83 mmole), water(10 mL), and lactic acid (1.13 g, 12.54 mmole). The ammonium vanadatedissolved without heating to form a green solution. The solution wasthen added to 6.21 g of the TiP₂O₇ 8×14 meshed material (0.028 mole) ina 100 mL single necked round bottomed flask. The flask was then placedon a roto-evaporator with a water bath set to 65° C. and rotated in thebath under ambient pressure for 20 minutes, the supernatant turned blueduring this time. The flask contents were then dried under vacuum at 65°C. and calcined at 450° C. in air for 16 hours to give yellow-greenirregular shaped particles.

Example 25

A supported catalyst comprising 5 mole % vanadium, 10 mole % titanium,and 10 mole % phosphorus was prepared in the following way: A whitecrystalline titanium pyrophosphate (TiP₂O₇) with a specific surface areaof 100 m²/g was first prepared according to the procedure described inI. C. Marcu et al., J. Mol. Catal., Vol. 203, pp. 241-250 (2003), thencrushed and sieved through an 8×14 mesh. A solution was prepared fromammonium vanadate (0.163 g, 0.0014 mole), TBALDH (1.67 g, 2.84 mmole),water (10 mL), and lactic acid (1.13 g, 12.54 mmole). The ammoniumvanadate dissolved without heating to form an orange solution. Thesolution was then added to 6.21 g of the TiP₂O₇ 8×14 meshed material(0.028 mole) in a 100 mL single necked round bottomed flask. The flaskwas then placed on a roto-evaporator with a water bath set to 65° C. androtated in the bath under ambient pressure for 20 minutes, thesupernatant turned green during this time. The flask contents were thendried under vacuum at 65° C. followed by addition of a solution of 85%H₃PO₄ (0.33 g, 2.86 mmole) in water (15 mL). The resulting suspensionwas then dried under vacuum on the roto-evaporator at 65° C., thencalcined at 450° C. in air for 16 hours to give yellow irregular shapedparticles.

Examples 26-37

The condensation reaction of acetic acid and trioxane (the formaldehydesource) for Examples 26-35, using the supported catalysts from Examples13-18 and 20-23, respectively, were performed following the proceduresof Comparative Example 1.

The condensation reactions of acetic acid and trioxane (the formaldehydesource) for Examples 36-37, using the supported catalysts from Examples24-25, respectively, were performed following the procedures of Example1.

The vapor-phase condensation experiments of Examples 26-37 wereperformed for three hours with a 12 acetic acid/1 trioxane molar ratiofeed (density 1.06 g/mL) at 325° C., 0.083 mL liquid feed/minute, and 80SCCM N₂. The performance of these catalysts is summarized in Tables 14and 15 below. These examples show that a supported V—Ti—P catalyst canbe produced using the water soluble redox-active organo-titaniumcompound. One skilled in the art recognizes that titanium chloride isnot amendable to impregnation on a solid support catalyst; thehydrochloric acid generated from titanium chloride hydrolysis can bedestructive to the support material.

TABLE 14 Example No. 26 27 28 29 30 31 32 Catalyst from Example 13 14 1516 17 18 20 No. Catalyst charge, g 5 5 5 5 5 5 5 Catalyst charge, mL 5.59.5 9.5 4.5 5 7.5 7.5 Product, g 13.738 14.391 13.576 13.638 13.71414.255 13.992 Reactants fed, g 15.836 15.836 15.836 15.836 15.836 15.83615.836 GC Results Acetone, wt % 0 0 0.18 0 0 0 0 MeOAc, wt % 0.21 0 0.580.17 0.16 0.09 0.16 MA, wt % 0 0 0 0 0 0 0.03 Water, wt % 7.46 6.31 6.934.11 5.25 6.12 6.22 HOAc, wt % 80.66 74.92 80.03 80.85 81.98 75.77 74.57Acrylic acid, wt % 11.81 16 4.9 6.71 12.83 15.12 16.02 HOPr 0.21 Totalknowns, wt % 100.35 97.23 92.62 91.84 100.22 97.09 97 Key Metrics Totalmole 1.5 2.1 0.6 0.8 1.6 2.0 2.1 acrylates/kg-hr % yield acrylic acid38.4 54.5 15.8 21.7 41.7 51.0 53.1 from H2CO % HOAc cony to AA 9.6 13.63.9 5.4 10.4 12.8 13.3 mmol HOAc 27.0 22.9 42.4 37.8 22.5 24.5 29.2unaccounted for % HOAc accountability 88.5 90.2 81.9 83.9 90.4 89.6 87.5

TABLE 15 Example No. 33 34 35 36 37 Catalyst from 21 22 23 24 25 ExampleNo. Catalyst charge, g 5 5 5 5 5 Catalyst charge, mL 9.5 9.5 10 9.759.75 Product, g 14.415 14.248 14.315 14.1 14.4 Reactants fed, g 15.83615.836 15.836 15.836 15.836 GC Results Acetone, wt % 0 0 0 0.06 0.09MeOAc, wt % 0.14 0.12 0.07 0.11 0.17 MA, wt % 0 0.02 0.02 0 0 Water, wt% 7.09 6.81 6.33 6.52 6.66 HOAc, wt % 78.01 77.92 74.74 73.77 75.36Acrylic acid, wt % 16.62 17.17 15.95 15.7 12.39 HOPr Total knowns, wt %101.86 102.04 97.11 98.13 97.07 Key Metrics Total mole 2.2 2.3 2.1 2.051.65 acrylates/kg-hr % yield acrylic acid 56.7 57.9 54.1 52.76 42.52from H2CO % HOAc cony to AA 14.2 14.5 13.5 13.09 10.55 mmol HOAc 13.615.3 24.4 30.17 28.36 unaccounted for % HOAc accountability 94.2 93.589.6 87.14 87.91

Example 38 Synthesis of V—Ti—P Catalyst

The catalyst was prepared by suspending ammonium metavanadate (19.455 g)in 300 mL of deionized water in a 500 mL single necked round bottomedflask. After heating at 70° C. for 1 hour, 85% orthophosphoric acid(105.4 g) was added at 70° C. over a 15 minute period to give a lightorange solution. Residual reactants were washed into the reaction flaskwith a minimal amount of water. The 50 wt. % titanium(IV) bis(ammoniumlactato)dihydroxide (TBALDH) solution (218.45 g) was added to a 1 Lthree necked kettle reactor equipped with a condenser and a mechanicalstirrer. The V/P solution was slowly poured into the TBALDH solution togive a pale green suspension. The V/P flask was rinsed with 30 mL ofwater and the contents added to the reaction flask. The mixture was thenstirred at 700 to 800 rpm at 100° C. for 16 hours. The water was thenremoved via distillation over 4 to 6 h and the resulting damp pale greensolid transferred to a ceramic dish and heated in air at 90° C. for 16hours in a muffle furnace. The resulting solid was crushed to fineparticles using a mortar and a pestle. This material was then calcinedfor 6 hours at 450° C. in air (60 SCCM) in a quartz tube to give palegreen catalyst particles. This material had a BET surface area of 37.9m²/g, was amorphous via X-ray diffraction and had a molar composition of1.0V-1.9Ti-5.2P, as determined by X-ray Fluorescence Spectroscopy. Thecatalyst was regenerated in air (100 SCCM) at 400° C. overnight aftereach experiment.

Examples 39-44 Synthesis of Methylene Diacetate

A 5 L round-bottom flask was fitted with a condenser, thermowell,overhead stirrer, inert gas bubbler, and heating mantle. To this flaskwas added 885 grams of paraformaldehyde followed by 3,324 mL of aceticanhydride. The mixture was stirred at room temperature and 12 mL ofconcentrated sulfuric acid was added. An exotherm heated the solution toapproximately 80° C. and then the heating mantle was turned on. Themixture was held at reflux for almost 10 hours and sampled periodicallyto check for completion by gas chromatography. Upon completion, 35 g ofNaOAc was added to the mixture to neutralize the sulfuric acid. Themixture was transferred to another flask and essentially pure MDA wasdistilled.

Condensation Reaction

The condensation reaction reactor was a 25 mm outer diameter (21 mminner diameter) quartz reactor tube with length=61 cm (24 inches). Heatto the reactor was provided by a Barnstead International electric tubefurnace (type F21100). The reactor was charged with 10 g of 8 by 14 meshV—Ti—P catalyst (Example 38). Liquid products were collected in anatmosphere-air cooled three necked flask. The base of the receiver flaskwas fitted with a stopcock to allow for draining of the liquid products.0.2 mL/minute of liquid methylene diacetate was vaporized and fed to thereactor which was heated at temperatures ranging from 190° C. to 310° C.Nitrogen was fed as a diluent at varying rates (SCCM) to produce acontact time between the total feed and catalyst of approximately onesecond. No water was fed to the reactor. The reaction was performed for4 hours. As a substantial exotherm was observed in the first 3 to 10minutes of the reaction, the first hour of reaction product wasdiscarded; liquid product was then collected after this first hour. Aliquid product sample from the last three hours of the experimental runwas collected, weighed and analyzed by gas chromatography. The resultsare presented in Table 16. In Table 16, the conversions are based onmoles of methylene diacetate converted to initial moles of methylenediacetate fed and the space time yield (STY) of acrylic acid is equal tomoles of acrylic acid produced per kg of catalyst per hour.

The vapor phase condensation experiment was repeated at temperaturesranging from 310° C. to 190° C., as given in Table 16. In Example 43,water was added to the feed at a molar ratio of one mole of methylenediacetate to one mole of water. For Example 43, the diluent gas flowrate was lowered to maintain a contact time between reactants and thecatalyst at approximately one second. The diluent for Examples 39-43 wasnitrogen, whereas the diluent for Example 44 was 6% oxygen and 94%nitrogen. The results are summarized in Table 16.

TABLE 16 Furnace Contact MDA Acrylic Acid STY MDA/ Temp. Time Conversion(moles/kg Paraformaldehyde Example Water (° C.) (sec.) (%) catalyst/hr)by-product 39 1/0 310 1.02 75 3.60 No 40 1/0 250 1.01 57 3.01 No 41 1/0220 1.02 35 1.40 No 42 1/0 190 1.02 25 0.70 No 43 1/1 250 1.02 97 3.30Yes 44 1/0 250 1.01 68 3.23 No

As can be seen from Examples 39-44 in Table 16, methylene diacetate canbe used as a feed to synthesize acrylic acid over a V—Ti—P catalyst. Asexpected, the STY of acrylic acid and methylene diacetate conversionsdecrease with temperature. The STY do not decrease in the presence of anequal molar amount of water when using methylene diacetate as a feed(comparing Examples 40 and 43).

Comparative Examples 9-18

The same reactor, catalyst, and experimental procedure as used inExamples 39-44 was repeated using acetic acid and formaldehyde as thefeed in place of methylene diacetate. The feed was a 2:1 acetic acid toformaldehyde (fed as trioxane) feed. The amount of water in each feed aswell as the temperatures are given in Table 17. The residence time wasmaintained constant at approximately 1 second for comparison purposes bychanging the diluent N₂ flow rate as the total feed rate (inclusive oforganics, water and diluent gas) changed based upon the amount of waterin a given example. The results are summarized in Table 17. In Table 17,the conversions are based on moles of formaldehyde, fed as trioxane,converted to initial moles of formaldehyde and the space time yield(STY) of acrylic acid is equal to moles of acrylic acid produced per kgof catalyst per hr. The diluent gas in Comparative Examples 9-17 wasnitrogen, whereas the diluent gas in Comparative Example 18 was 6%oxygen and 94% nitrogen.

TABLE 17 Comparative Acetic Acid/ Furnace Contact Formaldehyde AcrylicAcid STY Paraformaldehyde Example CH₂O/Water Temp. (° C.) Time (sec.)Conversion (%) (moles/kg catalyst/hr) by-product 9 2/1/3 310 1.00 201.17 No 10 2/1/3 280 1.00 8 0.38 No 11 2/1/3 250 1.00 10 0.05 No 122/1/1 310 0.97 34 2.24 No 13 2/1/1 280 1.03 26 0.94 No 14 2/1/1 250 1.0222 0.19 No 15 2/1/0 310 1.01 58 3.77 Yes 16 2/1/0 280 1.01 50 2.93 Yes17 2/1/0 250 1.01 33 1.43 Yes 18 2/1/0 250 1.01 41 1.52 Yes

This set of experiments evaluated the effect of water on STY by varyingtemperature and the molar ratio of acetic acid to formaldehyde to waterbetween 2/1/3, 2/1/1 and 2/1/0 while keeping the other reactorparameters constant. As shown in Table 17, water has a deleteriouseffect on conversion and space time yield. To attempt to maintain thesame space time yield of acrylic acid, the temperature must increasewith the presence of water in the feed solution; this is another majordrawback of using water. For example, a space time yield of 1.43 molesof acrylic acid/kg catalyst/hr (Comparative Example 17) was obtained at250° C. with a feed ratio of 2/1/0. By contrast, a lower space timeyield of 0.94 moles of acrylic acid/kg catalyst/hr (Comparative Example13) was obtained with the addition of water to give the feed ratio of2/1/1 even at the elevated temperature of 280° C.

To reduce the negative effects of water, trioxane can be employed in theliquid feed in the absence of additional water. Although this increasesthe reaction conversion and acrylic acid yield, generally the yields andconversions are substantially lower than the values obtained whenmethylene diacetate is used as the feed. This is observed even whenusing trioxane (without water addition) and acetic acid because the netsolution still contains one mole of latent molecular water. Thisunderscores the primary advantage of using methylene diacetate, i.e.,improvement in space time yields and conversions due to completeelimination of water in the feed. For example, at 250° C. the space timeyield of acrylic acid is 1.43 (Comparative Example 17) when using aconventional feed (defined as a solution of acetic acid and trioxane)whereas at the same temperature the space time yield is more than doubleat 3.01 (Example 40) when using a methylene diacetate feed.

Example 45

The ability of the V—Ti—P catalyst to be regenerated and yield the samereproducible experimental results is advantageous. The same catalystthat was used in Example 40 was regenerated overnight at 400° C. in acontinuous flow of 100 SCCM air. The same reactor, catalyst, andexperimental procedure as used in Example 40 were reproduced to giveExample 45. The results are summarized in Table 18. Examples 45 and 40demonstrate that the catalyst activity is reproducible after theregeneration step in air. The methylene diacetate conversion (57%) andthe space time yield of acrylic acid (3.01 moles/kg catalyst/hr) are thesame for each example. Moreover, paraformaldehyde was not formed ineither example as observed from a lack of solids accumulated in thecollection vessel.

TABLE 18 Furnace Contact MDA Acrylic Acid STY MDA/ Temp. Time Conversion(moles/kg Paraformaldehyde Example Water (° C.) (sec.) (%) catalyst/hr)by-product 40 1/0 250 1.01 57 3.01 No 45 1/0 250 1.01 57 3.01 No

Comparative Example 19

To verify the acrylic acid production was directly related to the V—Ti—Pcatalyst, the same reactor and experimental procedure as used inExamples 39-44 was repeated except the V—Ti—P catalyst powder wasremoved from the reaction tube and replaced with quartz chips. Just asthe V—Ti—P catalyst is treated prior to the reaction, the quartz chipswere calcined at 400° C. overnight in air. The results are given inTable 19. Comparative Example 19 demonstrates that the thermal treatmentof a quartz surface alone is insufficient for the equivalent productionof acrylic acid from a V—Ti—P catalyst.

TABLE 19 Furnace Contact MDA Acrylic Acid STY Comparative MDA/ Temp.Time Conversion (moles/kg Paraformaldehyde Example Water (° C.) (sec.)(%) catalyst/hr) by-product 19 1/0 310 — 3 0.09 No

Comparative Examples 20 and 21

To further illustrate that the production of acrylic acid with MDA as afeed is a unique ability of the V—Ti—P catalyst, the catalyst powder wasremoved from the reaction tube and replaced with 10 g anatase titaniumdioxide (TiO₂). Just as the V—Ti—P catalyst is treated prior to thereaction, the titanium dioxide material was calcined at 400° C.overnight in air. The same reactor and experimental procedure as used inExamples 39-44 was repeated. The results are given in Table 20. TheTable 20 data demonstrates that the TiO₂ catalyst did not produceappreciable amounts of acrylic acid. The STY's are lower, 0.03 and 0.42,for the anatase TiO₂, (Comparative Examples 20 and 21, respectively)than the corresponding values, 3.60 and 3.01, when using the V—Ti—Pcatalyst (Examples 39 and 40, respectively). This comparisondemonstrates that the anatase TiO₂ is not as desirable as the inventiveV—Ti—P catalyst for the conversion of methylene diacetate to acrylicacid.

TABLE 20 Furnace Contact MDA Acrylic Acid STY Comparative MDA/ Temp.Time Conversion (moles/kg Paraformaldehyde Example Water (° C.) (sec.)(%) catalyst/hr) by-product 20 1/0 310 1.02 24 0.03 No 21 1/0 250 1.0115 0.42 No

Comparative Example 22

To even further exemplify the ability of the V—Ti—P catalyst to catalyzethe production of acrylic acid from MDA, the V—Ti—P catalyst powder wasremoved from the reaction tube and replaced with 10 g of tungsten oxide(WO₃). Tungsten oxide was chosen since it is a typical oxide used forcatalyzing aldol chemistry. Just as the V—Ti—P catalyst is treated priorto the reaction, the tungsten oxide material was calcined at 400° C.overnight in air. The same reactor and experimental procedure as used inExamples 39-44 was repeated. The results are given in Table 21. TheTable 21 results show that the tungsten oxide's STY of 0.15 (ComparativeExample 22) is lower than the STY of 3.01 for the inventive V—Ti—Pcatalyst (Example 40) at catalyzing the aldol condensation chemistry forMDA.

TABLE 21 Furnace Contact MDA Acrylic Acid STY Comparative MDA/ Temp.Time Conversion (moles/kg Paraformaldehyde Example Water (° C.) (sec.)(%) catalyst/hr) by-product 22 1/0 250 1.01 7 0.15 No

Examples 46 and 47

To demonstrate the improved ability of the inventive V—Ti—P catalystsynthesized from a water-soluble, redox-active organo-titanium (Example38) over the ‘prior-art’ V—Ti—P catalyst where the titanium source isfrom a non-water-soluble tetrachlorotitanium compound (ComparativeExample 1), 10 g of the V—Ti—P catalyst described in Comparative Example1 was substituted in for the inventive V—Ti—P catalyst. This ‘prior-art’V—Ti—P material was calcined at 400° C. overnight in air before use andthe same reactor and experimental procedure was used as in Examples39-44. The results are summarized in Table 22. Examples 46 and 47 haveSTY of 1.58 and 1.51, respectively. These values are about 50% less thanthe corresponding STY, 3.60 and 3.01, of Examples 39 and 43,respectively.

TABLE 22 Furnace Contact MDA Acrylic Acid STY MDA/ Temp. Time Conversion(moles/kg Paraformaldehyde Example Water (° C.) (sec.) (%) catalyst/hr)by-product 46 1/0 310 1.02 17 1.58 No 47 1/0 250 1.01 13 1.51 No

Examples 48 and 49 Synthesis of Methylene Dipropionate

Methylene dipropionate (MDP) was produced from a refluxing mixture ofparaformaldehyde and propionic anhydride in the presence of a smallamount of sulfuric acid. The reaction was followed by using gaschromatography. Upon completion of the reaction, sodium propionate wasadded to the mixture to neutralize the sulfuric acid. The mixture wasdistilled to give 99% pure methylene dipropionate.

Condensation Reaction

The condensation reaction conditions were the same as those used for theacrylic acid in Examples 39-44 with adjustment of the N₂ flow rate tomaintain the 1 second residence time for the methylene dipropionate.Examples 48 and 49 presented here demonstrate the ability of methylenedipropionate to be used for the production of methacrylic acid; theresults are presented in Table 23. Examples 48 and 49 show that theV—Ti—P catalyst is highly active towards the production of methacrylicacid from methylene dipropionate (MDP) with 98 mole % and 63 mole %conversion and space time yields of 3.83 and 2.00, respectively, for themethacrylic acid product. The results of Table 23 demonstrate that theSTY of methacrylic acid from the conversion of methylene dipropionatedecrease with temperature.

TABLE 23 Furnace Contact MDP Methacrylic MDP/ Temp. Time Conversion AcidSTY Paraformaldehyde Example Water (° C.) (sec.) (%) (moles/kgcatalyst/hr) by-product 48 1/0 310 1.02 98 3.83 No 49 1/0 250 1.01 632.00 No

Comparative Examples 23-28

The vapor phase condensation experiments with a 2:1 propionic acid toformaldehyde (fed as trioxane) feed along with varying amounts of waterwere performed at temperatures ranging from 250° C. to 310° C., 0.2 mLliquid feed/minute for 4 hours. The residence time was maintainedconstant at approximately 1 second for comparison purposes by changingthe diluent N₂ flow rate. The performance of the catalyst is summarizedin Table 24. In Table 24, the conversions are based on moles ofpropionic acid converted to initial moles of propionic acid and thespace time yield (STY) of methacrylic acid is equal to moles ofmethacrylic acid produced per kg of catalyst per hr. The reactor andexperimental protocol used for these experiments was the same as thosedescribed in Examples 48 and 49. The catalyst was the same V—Ti—Pmaterial made in Example 38 but was regenerated prior to each experimentby an overnight calcination step in air at 400° C.

TABLE 24 Propionic Furnace Contact Methacrylic Comparative Acid/CH₂O/Temp. Time Propionic Acid Acid STY Paraformaldehyde Example Water (° C.)(sec.) Conversion (%) (moles/kg catalyst/hr) by-product 23 2/1/3 3101.02 12 0.16 No 24 2/1/3 250 1.03 13 0.01 No 25 2/1/1 310 1.03 13 0.55No 26 2/1/1 250 1.05 10 0.04 No 27 2/1/0 310 1.00 9 0.73 Yes 28 2/1/0250 1.02 3 0.18 Yes

The space time yields of methacrylic acid from the conversion ofmethylene dipropionate over the V—Ti—P catalyst were unexpected.Comparative Example 30 shows the STY of methacrylic acid at 250° C. is0.18 when using a conventional feed of propionic acid and trioxane but aspace time yield of 2.00 is obtained at the same temperature when usinga feed of methylene dipropionate (Example 49). This more than eleventimes higher STY is a benefit of using methylene dipropionate as thefeed.

Tables 23 and Table 24 underscore the differences in space time yieldsdepending on whether the production of methacrylic acid uses aconventional feed comprising varying ratios of propionic acid toformaldehyde to water of 2/1/3, 2/1/1 and 2/1/0 or the production ofmethacrylic acid with methylene dipropionate as the feed. When theconventional feed is used (Table 24, Comparative Examples 23-28) theSTY's ranged from 0.01 to 0.73 while when the methylene dipropionatefeed is used (Table 23, Examples 48 and 49) the STY's ranged from 2.00to 3.83.

Comparative Example 29

To verify the methacrylic acid production was directly related to theV—Ti—P catalyst, the same reactor and experimental procedure as used inExamples 48 and 49 was repeated except the V—Ti—P catalyst powder wasremoved from the reaction tube and replaced with quartz chips. Just asthe V—Ti—P catalyst was treated prior to the reaction, the quartz chipswere calcined at 400° C. overnight in air. The results are given inTable 25. The Table 25 data demonstrates that the thermal treatment of aquartz surface alone is insufficient to prepare acrylic acid from aV—Ti—P catalyst and methylene dipropionate.

TABLE 25 Furnace Contact MDP Methacrylic Comparative MDP/ Temp. TimeConversion Acid STY Paraformaldehyde Example Water (° C.) (sec.) (%)(moles/kg catalyst/hr) by-product 29 1/0 310 — 0 0 —

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

What is claimed is:
 1. A process for preparing acrylic acid comprising:contacting methylene diacetate and a diluent gas with a condensationcatalyst under vapor-phase condensation conditions to obtain the acrylicacid; wherein the condensation catalyst comprises a mixed oxide ofvanadium (V), titanium (Ti), and phosphorus (P); wherein the methylenediacetate has the general formula (I):

and wherein R is hydrogen.
 2. The process according to claim 1, whereinthe condensation catalyst has the formula VTi_(a)P_(b)O_(c), wherein ais a number from 0.3 to 6.0, b is a number from 2.0 to 13.0, and c isthe number of atoms required to satisfy the valences of the componentsother than oxygen.
 3. The process according to claim 2, wherein thetitanium component is the residue of a water-soluble, redox-activeorgano-titanium compound.
 4. The process according to claim 1, whereinthe organo-titanium compound comprises titanium(IV) bis(ammoniumlactate)dihydroxide.
 5. The process according to claim 1, wherein thecontacting occurs with 1 mol % to 90 mole % diluent gases, based on thetotal moles of the methylene diacetate and the diluent gas.
 6. Theprocess according to claim 1, wherein the diluent gas comprises fromabout 0.5 mole % to about 20 mole % oxygen, based on the total moles ofdiluent gas.
 7. The process according to claim 1, wherein the space timeyield of the 2,3 unsaturated carboxylic acid is from about 0.1 to about200 moles of 2,3 unsaturated carboxylic acid per kg catalyst per hour.8. A process for preparing methacrylic acid comprising: contactingmethylene dipropionate and a diluent gas with a condensation catalystunder vapor-phase condensation conditions to obtain the acrylic acid;wherein the condensation catalyst comprises a mixed oxide of vanadium(V), titanium (Ti), and phosphorus (P); wherein the methylenedipropionate has the general formula (I):

and wherein R is a methyl group.
 9. The process according to claim 8,wherein the condensation catalyst has the formula VTi_(a)P_(b)O_(c),wherein a is a number from 0.3 to 6.0, b is a number from 2.0 to 13.0,and c is the number of atoms required to satisfy the valences of thecomponents other than oxygen.
 10. The process according to claim 9,wherein the titanium component is the residue of a water-soluble,redox-active organo-titanium compound.
 11. The process according toclaim 8, wherein the organo-titanium compound comprises titanium(IV)bis(ammonium lactate)dihydroxide.
 12. The process according to claim 8,wherein the contacting occurs with 1 mol % to 90 mole % diluent gases,based on the total moles of the methylene diacetate and the diluent gas.13. The process according to claim 8, wherein the diluent gas comprisesfrom about 0.5 mole % to about 20 mole % oxygen, based on the totalmoles of diluent gas.
 14. The process according to claim 8, wherein thespace time yield of the 2,3 unsaturated carboxylic acid is from about0.1 to about 200 moles of 2,3 unsaturated carboxylic acid per kgcatalyst per hour.
 15. A process for preparing a 2,3-unsaturatedcarboxylic acid, comprising: contacting a methylene dialkanoate and adiluent gas with a condensation catalyst under vapor-phase condensationconditions to obtain the 2,3-unsaturated carboxylic acid, wherein thecondensation catalyst comprises a mixed oxide of vanadium (V), titanium(Ti), and phosphorus (P); wherein the titanium component is the residueof a water-soluble, redox-active organo-titanium compound comprisingtitanium(IV) bis(ammonium lactate)dihydroxide; wherein the methylenedialkanoate has the general formula (I):

and wherein R is selected from the group consisting of hydrogen, methyl,ethyl, propyl, and isopropyl.
 16. The process according to claim 15,wherein the condensation catalyst has the formula VTi_(a)P_(b)O_(c),wherein a is a number from 0.3 to 6.0, b is a number from 2.0 to 13.0,and c is the number of atoms required to satisfy the valences of thecomponents other than oxygen.
 17. The process according to claim 15,wherein R is methyl, wherein the methylene dialkanoate is methylenedipropionate.
 18. The process according to claim 15, wherein R ishydrogen, wherein the methylene dialkanoate is methylene diacetate. 19.The process according to claim 15, wherein the diluent gas comprisesfrom about 0.5 mole % to about 20 mole % oxygen, based on the totalmoles of diluent gas.
 20. The process according to claim 15, wherein thespace time yield of the 2,3 unsaturated carboxylic acid is from about0.1 to about 200 moles of 2,3 unsaturated carboxylic acid per kgcatalyst per hour.